Journal of Colloid and Interface Science 614 (2022) 460–467 Contents lists available at ScienceDirect Journal of Colloid and Interface Science journal homepage: www.elsevier.com/locate/jcis Enhanced arsenite removal by superparamagnetic iron oxide nanoparticles in-situ synthesized on a commercial cube-shape sponge: adsorption-oxidation mechanism Xiang-Yang Lou a, Roberto Boada a,⇑, Laura Simonelli b, Manuel Valiente a a GTS-UAB Research Group, Department of Chemistry, Facultat de Ciències, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain b ALBA Synchrotron, Carrer de la llum 2-26, Cerdanyola del Vallès, 08290 Barcelona, Spain h i g h l i g h t s g r a p h i c a l a b s t r a c t  Commercial cube-shaped sponge loaded with superparamagnetic iron oxide nanoparticles (SPION) was successfully synthesized and used for As(III) removal.  The adsorption capacity of the SPION loaded in the composite was 935.0 mgg1 Fe with 1000 mgL-1 initial concentration, much higher than previously reported values.  Arsenic K-edge XAS measurements revealed that As(III) was partially oxidized to less toxic As(V) upon adsorption.  Proposed mechanism indicates that As(III) was first adsorbed on the surface of adsorbent and then oxidized by the OH generated from Fe(III) and the –OH groups present in the adsorbent. a r t i c l e i n f o a b s t r a c t Article history: Hypothesis: The easy aggregation of superparamagnetic iron oxide nanoparticles (SPION) greatly reduces Received 24 November 2021 their adsorption performance for removing arsenic (As) from polluted water. We propose to exploit the Revised 17 January 2022 porosity and good diffusion properties of a cube-shaped cellulose sponge for loading SPION to reduce the Accepted 18 January 2022 aggregation and to develop a composite adsorbent in the cm-scale that could be used for industrial appli- Available online 21 January 2022 cations. Experiments: SPION were in-situ synthesized by co-precipitation using a commercial cube-shaped sponge Keywords: (MetalZorbÒ) as support. The morphology, iron-oxide phase, adsorption performance and thermody- Arsenite removal Adsorption-oxidation namic parameters of the composite adsorbent were determined to better understand the adsorption pro- superparamagnetic iron oxide nanoparticles cess. X-ray absorption spectroscopy (XAS) was used to investigate the chemical state of the adsorbed As (SPION) (III). Commercial cube sponge Findings: The adsorption of the supported SPION outperforms the unsupported SPION (ca. 14 times X-ray absorption spectroscopy higher adsorption capacity). The modelling of the adsorption isotherms and the kinetic curves indicated that chemisorption is controlling the adsorption process. The thermodynamic analysis shows that the ⇑ Corresponding author. E-mail address: roberto.boada@uab.cat (R. Boada). https://doi.org/10.1016/j.jcis.2022.01.119 0021-9797/Ó 2022 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Xiang-Yang Lou, R. Boada, L. Simonelli et al. Journal of Colloid and Interface Science 614 (2022) 460–467 adsorption retains the spontaneous and endothermic character of the unsupported SPION. The XAS results revealed an adsorption-oxidation mechanism in which the adsorbed As(III) was partially oxidized to less toxic As(V) by the hydroxyl free radical (OH) generated from Fe(III) species and by the hydroxyl groups. Ó 2022 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction MetalZorbÒ sponge is an open-celled cellulose cube-shaped material with the properties of high porosity, high flexibility, large Arsenic (As) contamination has become a worldwide problem specific surface area and low price, which is beneficial as the sup- due to its high toxicity and carcinogenicity [1]. As is released into port for nanoparticles. This material is claimed to contain free the environment by both natural processes and anthropogenic available iminodiacetate groups to interact with superparamag- activities such as rock weathering, mineral extraction, wood netic iron oxide nanoparticles (SPION) by chelation. In this work, preservation, pigments [2]. In nature waters, As is mainly found we propose this commercial cube-shaped MetalZorbÒ sponge to in inorganic forms, As(III) (arsenite) and As(V) (arsenate) [3]. As support SPION as a composite material for the removal of As(III) (III) is mostly present in underground waters whereas As(V) is from aqueous solutions. The adsorption performance of this com- mostly found in surface water [4]. Regarding the toxicity, As(III) posite material was studied and compared with the unsupported is 60-fold more toxic than As(V) [5]. Short-term exposure to high SPION in powder form. Furthermore, our X-ray absorption spec- concentrations of As can be fatal, while long-term exposure to troscopy study at different depths of the cube adsorbent has trace concentrations of As can cause skin, lung, bladder cancers allowed us to investigate the adsorption mechanisms at molecular [6]. As can be transferred into the food chain through grain crops scale and the redox processes that may take place upon adsorption. irrigated with As contaminated water and through seafood living in arsenic-containing water [7]. Exposure through contaminated 2. Materials and methods drinking water is another direct pathway to humans [8]. The World Health Organization (WHO) has established a maximum concen- 2.1. Materials tration of As in drinking water of 10 lgL-1 [9]. However, still many people are exposed nowadays to high levels of As pollution in some All reagents used were of analytical grade. Iron chloride hex- parts of the world, particularly in developing countries [10]. There- ahydrate (FeCl36H2O) and ferrous chloride tetrahydrate (FeCl2- fore, the effective removal of As from water, and in particular As 4H2O) were used in the synthesis of SPION and sponge-loaded (III), is markedly important for environmental protection and SPION. Sodium arsenite (NaAsO2) was used as the source of As human health. (III). A 1000 mgL-1 As(III) stock solution was initially prepared, Among all the techniques available for As removal, adsorption is and then diluted to the required concentration. Hydrogen chloride considered to be one of the most promising methods because of its (HCl) and sodium hydroxide (NaOH) were used to adjust the pH advantages of being fast, easy to operate, environmentally friendly during adsorption experiments. and cost-effective [11]. In recent years, magnetic iron oxide Commercial cube-shaped MetalZorbÒ adsorbent was kindly nanoparticles have attracted large attention due to their specific supplied by CleanWay Environmental Partners, Inc. (Portland, affinity to arsenic over other metals [12], large specific surface area USA). The material is an open-celled cellulose sponge (hereafter [13] and easy separation from aqueous solution [14–16]. Various referred simply as ‘‘sponge”) as described in our previous publica- adsorption studies using magnetic iron oxide-based adsorbents tions [29]. The averaged dimensions of the cube are for arsenic removal have been reported [17–20]. However, the (length  width  height): 12.8 ± 1.8  10.1 ± 1.1  7.3 ± 1.3 m aggregation of the nanoparticles in water negatively affects their m. Each cube has an average weight of 0.20 ± 0.02 g. adsorption performance [21–23] For instance, Liu et al. [22] syn- thesized magnetic iron oxide nanoparticles for As removal with 2.2. Synthesis of the adsorbents and characterization an average diameter of 34 nm; however, particles aggregated a lot under adsorption conditions reaching sizes over lm-size which SPION were synthesized by the co-precipitation method [30]. In greatly reduced the available surface area for adsorption. the synthesis of sponge-loaded SPION, raw sponge was pre-treated To overcome this issue, materials like activated carbon [24], fly and deprotonated following the suggestion from the manufacturer ash [25], and biomass [26] have been traditionally used as supports and afterwards the nanoparticles were synthesized in-situ. Details for nanoparticles. Although this approach helps in reducing the about the synthesis methods for SPION and sponge-loaded SPION aggregation and provides good adsorption results, most of these can be found in section S1 of the Support information (SI). Regard- composite materials reported are in powder form and, therefore, ing the synthesis mechanisms, the iminodiacetate groups present they are not suitable for direct industrial use. In addition, they on the surface of the sponge act as anchor points for the nanopar- are very difficult to recover when used for on-site environmental ticles by chelation at the onset of the nucleation stage. remediation applications. Indeed, when used in a fixed-bed col- The surface area data of unsupported SPION calculated from N2 umn, the powder adsorbents tend to clog the column, and restrict adsorption analysis is 92.3 m2g1. Cube adsorbents were split into the flow rate which limits their practical use. To overcome this three regions (surface, quarter, and center) to get information at issue, some powders have been loaded on membranes and hybrid different depths, as shown in Fig. S1. The SEM and TEM images methods combining adsorption with membrane filtration have confirmed the successful loading of SPION on the porous structures been developed [27]. This alternative approach greatly reduces of the sponge (see top panel of Fig. S2). The average nanoparticle the aggregation of nanoparticulate adsorbents; however, the com- size calculated by Image-pro plus software (Media Cybernetics, Sil- posite material based on membranes have a much higher cost, and ver Spring, USA) from the TEM images were 12.7 and 13.8 nm for it has other disadvantages such as membrane fouling that must be surface and center parts, respectively (see middle and bottom pan- taken into consideration [28]. els of Fig. S2). Hence, the size of the SPION loaded on the sponge 461 Xiang-Yang Lou, R. Boada, L. Simonelli et al. Journal of Colloid and Interface Science 614 (2022) 460–467 has been greatly reduced respect to the effective particle size of the decanting the aqueous solution, the solid was washed three times aggregated unsupported SPION (100 nm). Unfortunately, some with Milli-Q water, afterwards, the adsorbents were dried in an degree of aggregation is still present in the composite. The slightly oven at 50 °C for 24 h. Arsenic trioxide, As(III), and arsenic pentox- different particle size of the SPION at surface and center parts ide, As(V), were used as reference materials. All samples and refer- might be due to the slightly reduction of the diffusion in the inner ences were milled and pressed into pellets for performing the part of the cube respect to the surface part which may promote a measurements. rapid growth of the particles. X-ray absorption near edge structure The XAS experiment at the As K-edge was carried out at BL22 (XANES) spectra of Fe K-edge collected on SPION, sponge-loaded CLÆSS beamline of ALBA CELLS synchrotron using a Si(3 1 1) double SPION (surface), sponge-loaded SPION (center), indicated that the crystal monochromator [31]. Measurements of sponge and SPION iron oxide phase was maghemite (c-Fe2O3) (see Fig. S3). In addi- samples were performed in fluorescence mode using a multi- tion, the XANES comparison of old and fresh composite material element silicon drift detector, while measurements for sponge- showed that iron oxidation state was stable over time (see loaded SPION and As references were collected in transmission Fig. S4). The loading amount of the SPION was around 2.6 wt% in mode using ionization chambers. To reduce the self-absorption the composite as determined by ICP-MS analysis. effect, SPION powder was homogeneously mixed with cellulose using a SPION:cellulose ratio of 1:10. Special care was taken when 2.3. Adsorption experiments setting up the fluorescence measurements to minimize the damp- ing effect due to the dead-time. The measurements were carried Adsorption experiments were performed by putting 0.20 g out at liquid nitrogen temperature to minimize any possible radi- adsorbent (either SPION, cube sponge or cube sponge-loaded ation damage. XAS data analysis was performed according to stan- SPION) in contact with 25.0 ml of As(III) solution. The tubes were dard procedures using ATHENA software of the Demeter package agitated mechanically at 300 rpm using a rotary shaker. Adsorption [32]. experiments were performed at different temperatures by putting the shaker inside of an incubator. Adsorption experiments with dif- ferent initial concentrations were performed for concentrations within the range 10–1000 mgL-1 As(III) at pH 7.0 shaking during 3. Result and discussion 120 min; experiments at different contact times (1–480 min) were performed at pH 7.0 and using a 200 mgL-1 initial concentration; 3.1. Adsorption performance experiments at different pH values were performed by adjusting the pH from 3.0 to 10.0 with 200 mgL-1 initial concentration and Batch experiments were performed to study the adsorption agitating during 120 mins. behavior of the materials. Different parameters (initial concentra- After adsorption, for SPION, the nanoparticles were magneti- tion, contact time, and pH) that affect As(III) adsorption were cally separated. In the case of sponge or sponge-loaded SPION, investigated. The adsorption capacities of the unsupported SPION, the adsorbent was separated by decanting the aqueous solution. sponge-loaded SPION (composite material) and SPION in compos- The amount of As(III) adsorbed was determined as the difference ite (considering only the mass of the loaded SPION in the compos- of the remaining As(III) in the solution from the initial one. The ite) were compared. As seen in (Fig. 1a), the adsorption capacity of As(III) concentration was determined by applying the molybde- SPION and sponge-loaded SPION increased with As(III) initial con- num blue spectrophotometric method after oxidating the As(III) centration. In contrast, the adsorption of As(III) in sponge was to As(V) with potassium permanganate (KMnO4) (further details below the detection limit of the colorimetric method used and can be found in section S4 in SI). The adsorption capacity at equi- therefore it can be considered negligible. This means that the librium was calculated using the following equation: sponge acts mainly as a support for reducing the aggregation of SPION. Our results show that the sponge-loaded SPION composite V q e ¼ ð Co  Ce Þ ð1Þ has less adsorption capacity than the unsupported SPION, however, m when considering only the small mass fraction of SPION in the where qe (mgg1) is the adsorption capacity, V (L) is the volume of composite, 2.6 wt%, there is an enhancement of the adsorption the arsenic solution, m (g) is the dry weight of the adsorbent, Co and capacity over one order of magnitude respect to the unsupported Ce (mgL-1) are initial and equilibrium concentrations of As(III) solu- SPION. For instance, at the maximum initial concentration used tion, respectively. (1000 mgL-1), the adsorption capacity of the composite per gram of SPION is 655.0 mgg1 for the composite and only 45.3 mgg1 2.4. Isotherm and kinetic modeling for the unsupported SPION. In other words, the SPION loaded in the sponge displays ca. 14 times the adsorption capacity of the To further understand the As(III) adsorption behavior, experi- unsupported SPION. This difference is due to the greatly reduced mental adsorption isotherms were fitted with Langmuir, Fre- aggregation of the nanoparticles when loading the SPION on the undlich and Temkin isotherm models. Separately, the adsorption sponge as can be seen in the TEM images (Fig. S2). data collected at different contact times were fitted to pseudo- The dependence of adsorption capacity respect to the contact first order and pseudo-second order kinetic models. Detailed infor- time is shown in (Fig. 1b). There is a sharp increase in the adsorp- mation about these isotherm and kinetic models can be found in tion capacity during the initial 60 min. This can be attributed to the section S5 of the SI. large number of adsorption sites initially available on the surface of the adsorbent. When normalizing by the mass fraction of the 2.5. Synchrotron radiation based XAS analysis loaded SPION, the adsorption capacity of SPION in the composite material reaches 295.6 mgg1. This is ca. 14 times higher than X-ray absorption spectroscopy (XAS) technique was used to the one of the unsupported SPION (21.0 mgg1). study the oxidation state of As after adsorbed on the different The adsorption behavior at equilibrium did not show a signifi- adsorbents (SPION, sponge and sponge-loaded SPION). An initial cant dependence with the pH between 3.0 and 10.0, see Fig. S5. concentration of 200 mgL-1 As(III) and a contact time of 120 min This is due to the fact that uncharged H3AsO3 (pKa = 9.2) is the were used. The effect of the adsorption temperature was also stud- main As(III) species. Therefore, As(III) cannot be adsorbed by elec- ied by performing adsorption experiments at 293 and 343 K. After trostatic interaction [33,34]. 462 Xiang-Yang Lou, R. Boada, L. Simonelli et al. Journal of Colloid and Interface Science 614 (2022) 460–467 Fig. 1. As(III) adsorption capacity of SPION, sponge-loaded SPION and SPION in composite: initial concentration (a) and contact time (b). 3.2. Adsorption isotherm modeling between the SPION-As(III) ion surface than sponge-As(III) surface. This result is consistent with our adsorption experiment data The results for the As(III) adsorption isotherm modeling for showing that the sponge does not adsorb As(III). SPION, sponge-loaded SPION and SPION in composite are shown in Fig. 2 and Table S1. Langmuir, Freundlich and Temkin isotherm 3.3. Kinetics models were used. Relatively good fits (R2 > 0.90) were found for the three models for all the adsorbents. For unsupported SPION, Kinetic parameters were determined to assess the efficiency the best fit was found for the Temkin model and the mechanism of the adsorption process [36,37]. The fitting (Temkin > Langmuir > Freundlich). For the composite material results using the pseudo-first order kinetic model and pseudo- and for the supported SPION, the Langmuir model has a higher cor- second order kinetic model are displayed in Fig. 3 and Table S2. relation coefficient than the Temkin model The results show that the As(III) adsorption process on the adsor- (Langmuir > Temkin > Freundlich), however, the heterogeneity of bents is best interpreted by the pseudo-second order kinetic the composite adsorbent should be taken into consideration and model. This indicates that chemisorption is driving the adsorption therefore the Langmuir model is not suitable for these adsorbents process rate, which is in line with the results obtained from the iso- since it considers single layer and homogeneous adsorption. Hence, therm modelling. considering both the fitting results and the characteristics of the materials, the Temkin model provides the best agreement for all 3.4. Thermodynamic determinations adsorbents. This model explicitly considers the adsorbent–adsor- bate interactions [35]. As can be seen from the fitting results Thermodynamic parameters such as Gibbs free energy change (Fig. S1), the values of bT (related to the heat of adsorption) for (DGo), enthalpy change (DHo) and entropy change (DSo) were unsupported SPION, sponge-loaded SPION and SPION in composite determined to predict the feasibility and thermodynamic nature are all positive, which implies that in all the cases the adsorption is of the adsorption process [38,39]. The calculated method is dis- exothermic. In addition, the AT (related to the binding energy) played in section S7 and the thermodynamic parameters deter- value of unsupported SPION is substantially larger than that of mined are displayed in Table 1. the composite material, which means a stronger interaction The adsorption of As(III) on the composite adsorbent has nega- tive DGo, positive DH° and positive DS° as SPION. The negative DGo values indicate that the adsorption of As(III) onto SPION is sponta- neous. The values of DH° for SPION and sponge-loaded SPION are 10.50 and 4.68 kJmol1, respectively, which indicates that the As (III) adsorption on both adsorbents is an endothermic process. The positive DS° likely resulted from the release of orderly struc- tured hydration water and subsequent increase in randomness with increased concentration of adsorbed As(III) on the solid sur- face [40,41]. 3.5. Compare of the adsorption capacity with similar adsorbent system Considering the Fe content in the adsorbents, the equilibrium adsorption capacities of unsupported SPION and supported SPION at 1000 mgL-1 As(III) initial concentration are 64.7 and 935.0 mgg1 Fe, respectively. This indicates that the loading of SPION on the sponge can significantly improve the adsorption capacity respect to the unsupported SPION. This can be attributed to the less aggregation of the SPION when loaded in the sponge Fig. 2. As(III) adsorption isotherm modeling for SPION, sponge-loaded SPION and support which increases the effective surface available for the SPION in composite at 293 K. adsorption process. 463 Xiang-Yang Lou, R. Boada, L. Simonelli et al. Journal of Colloid and Interface Science 614 (2022) 460–467 Fig. 3. Kinetic modeling for As(III) adsorption on SPION, sponge-loaded SPION and SPION in composite: Pseudo-first order model (a) and Pseudo-second order model (b). Table 1 Thermodynamic parameters for As(III) adsorption on SPION, sponge-loaded SPION and SPION in composite. Adsorbent Temperature(K) DGo DH o DSo (kJmol1) (kJmol1) (Jmol1K1) SPION 293 16.43 10.50 91.88 318 18.73 343 21.03 Sponge-loaded SPION 293 10.68 4.68 52.39 318 11.99 343 13.30 SPION in composite 293 19.60 4.68 82.82 318 21.67 343 –23.74 In addition, the adsorption capacities of both unsupported 3.6. As K-edge XAS measurements SPION and supported SPION are compared with their similar sys- tem reported adsorbents, the results are listed in Table 2. In our Due to the different toxic risks associated with the As species case, we are not quoting the maximum adsorption capacity extrap- [47], it is important to understand the fate of adsorbed As(III) olated from the isotherm modelling but the adsorption capacity for and to discern any possible redox processes that may take place an initial As(III) concentration of 1000 mgL-1, and this value would upon adsorption. Indeed, the oxidation state and the speciation be lower than the hypothetical maximum adsorption capacity. We of As determine its toxicity and mobility in the environment can clearly see, the adsorption capacity of unsupported SPION is [48]. In that respect, X-ray absorption near-edge structure (XANES) significantly higher when compared with both the adsorption experiments were performed to investigate the coordination envi- capacities of commercial GEH-102 [42] and laboratory synthesized ronment and the chemical state of As(III) adsorbed on SPION, magnetite nanoparticles by Liu et al. [22]. A significant improve- sponge and sponge-loaded SPION. The influence of the different ment in adsorption capacity of SPION supported by cube sponge temperatures and the different depths of cube adsorbents (C, Q, was also found when compared with other reported Fe-based com- S) were also studied. (Fig. 4a) shows the comparison of the As K- posite powder adsorbents [43–46]. Besides, one of the additional edge XANES spectra of the adsorbent materials with the reference advantages of our cube sponge-based composite is that, once compounds for As(III), arsenic trioxide, and As(V), arsenic pentox- exhausted, it can be easily compressed into a very small volume, ide. The As reference compounds display a markedly different thus facilitating its transport and waste disposal. spectral profile. The pentoxide is shifted  3.7 eV towards high Table 2 Comparison of the As(III) adsorption capacities of unsupported SPION and SPION in composite with similar Fe-based systems. Support Size Fe content (wt%) Iron phase qe (mgg1 Fe) Reference None 12.0 nm 70.0 c-Fe2O3 64.7 * This work Cube sponge 13x10x7 mm 1.8 c-Fe2O3 935.0 * This work None 34 nm 72.4 Fe3O4 23.0 [22] None 0.3–2 mm 52–62 Fe(OH)3 and 33.3 [42] b-FeO(OH) Cork 0.8–2 mm 2.4 iron (oxy)hydroxides 204.2 [43] Cellulose 0.02 mm 36 Fe2O3 64.3 [44] Alginate beads 0.5 mm 30 2-line ferrihydrite 159.3 [45] Polyurethane foam 6 nm 19.3 Fe3O4 178.7 [46] (*) at 1000 mgL-1. 464 Xiang-Yang Lou, R. Boada, L. Simonelli et al. Journal of Colloid and Interface Science 614 (2022) 460–467 Fig. 4. As K-edge XAS spectra of adsorbents after adsorbing As(III) at different temperatures (a) and corresponding peak fitting results (b). Arsenic trioxide and pentoxide compounds are also included for comparison and used for peak fitting references. energy with respect to the trioxide. In addition, the white-line fea- respect to negligible As(III) adsorbed on the sponge. On the other ture (first resonance after the absorption rising edge) appears at hand, SPION showed a larger amount of As(V) than sponge- 11875.5 and 11871.7 eV for pentoxide and trioxide, respectively. loaded SPION. This can be related to the low loading of the c- By direct comparison of the position of the absorption edge and Fe2O3 nanoparticles in the composite material (2.6 wt%). In other the white-line, we found that some of the As(III) was oxidized to words, the As:Fe ratio in the composite is much larger than in As(V) upon adsorption. This oxidation was related to the existence the unsupported SPION, which turns into less available Fe(III) spe- of the reactive oxygen species (ROS), especially hydroxyl free rad- cies to contribute to the As(III) oxidation process after adsorption. ical (OH) and hydrogen peroxide (H2O2) generated by Fe(III) In all the materials, the oxidization of As(III) to As(V) was more [22,49] and the hydroxyl groups (–OH) [50] present in SPION and favorable at lower temperatures since the decomposition of H2O2 sponge adsorbents. at higher temperatures results in a decrease of OH [51]. However, Furthermore, no As(V) ions were found in the aqueous solution the difference in the oxidation of sponge-loaded SPION caused by before and after adsorption, implying that this oxidation reaction the temperature was very small (only  2%). This can be related mainly occurred on the surface of the adsorbent. Thus, a combina- with the small mass loading of SPION in the composite as men- tion of adsorption-oxidation mechanisms is proposed. Under neu- tioned above. After adsorption, the amount of –OH functional site tral and aerobic conditions, As(III) is firstly adsorbed on the surface available in the loaded SPION is much lower than in the case of of the adsorbents, and then oxidized by the generated ROS from unsupported SPION. the composite material. The proposed mechanism is shown in When comparing different depths of the cube adsorbents, for Fig. 5. sponge, the As(III) adsorbed in center part showed a higher amount In addition, to unravel the two As species, a peak fitting analysis of As(V) species due to the diffusion constraints that increase of the XANES spectra was performed (see details in section S8). The towards the center of the cube, hence, reducing the recirculation results are displayed in (Fig. 4b) and Table S5. When comparing the of hydroxyl free radicals and favoring the interaction. However, different adsorbents it was found that the largest amount of As(III) for sponge-loaded SPION, the As(III) oxidation reaction is con- oxidized to As(V) was taking place in sponge, 30–60%. This can be trolled by the mass of SPION, which is rather constant in the whole due to the large density of functional sites that can oxidize As(III) cube and yields similar As(V) conversion in all parts of the cube. In addition, it is important to bear in mind that the amount of As adsorbed in sponge is almost negligible and, therefore, neither the effects of the temperature nor the penetration depth will be significantly reflected in the oxidation process taking place in the cube composite adsorbent. 4. Conclusions In contrast to the broadly reported iron-based composite adsor- bents in powder form [52–54], here we have reported the synthe- sis, characterization and molecular adsorption mechanism for a cm-scale cube-shaped composite adsorbent. This adsorbent mate- rial is composed by superparamagnetic iron oxide nanoparticles (SPION) in-situ co-precipitated in a commercial open-cellulose sponge. Our results show that the nanoparticle aggregation is greatly reduced in the composite which yields a much better As (III) adsorption performance than in the case of the unsupported SPION. Hence, the composite material retains the advantageous Fig. 5. Proposed mechanism of the As(III) adsorption-oxidation process taking place properties of SPION for As adsorption. Moreover, the results from on the surface of the composite adsorbent. our XAS study indicate that, once adsorbed, the highly toxic and 465 Xiang-Yang Lou, R. Boada, L. Simonelli et al. Journal of Colloid and Interface Science 614 (2022) 460–467 carcinogenic As(III) is partially oxidized to less toxic As(V), which is Methanolic Extract via Downregulation of MAPK/Caspase-3 Pathway, Evidence-Based Complement. Altern. Med. 2017 (2017) 1–12, https://doi.org/ desirable for the treatment of As(III)-contaminated waters. 10.1155/2017/8137627. Researchers using unsupported nanoparticles or composite pow- [5] N.S. Ferreira, L.H.B. Oliveira, V. Agrelli, A.F. de Oliveira, A.R.A. Nogueira, A. ders have reported similar results [22,55], however, our study Oliveira, M.H. Gonzalez, Bioaccumulation and acute toxicity of As(III) and As has also revealed that this As(III) oxidation is not temperature- (V) in Nile tilapia (Oreochromis niloticus), Chemosphere 217 (2019) 349–354, https://doi.org/10.1016/j.chemosphere.2018.11.013. dependent. In addition, a similar oxidation state of the adsorbed [6] A. Mehri, Trace elements in human nutrition (II) - An update, Int. J. Prev. Med. As was found at different cube depths which demonstrates that 11 (2020) 2, https://doi.org/10.4103/ijpvm.IJPVM_48_19. the same adsorption process occurs at the different parts of the [7] K. Karimyan, M. Alimohammadi, A. Maleki, M. Yunesian, R.N. Nodehi, A.R. Foroushani, The mobility of arsenic from highly polluted farmlands to wheat: cube composite. This is due to the good diffusion properties of Soil-Plant transfer model and health risk assessment, L. Degrad. Dev. 31 (12) the sponge material and the rather homogeneity of the SPION (2020) 1560–1572, https://doi.org/10.1002/ldr.3552. loaded in the porous sponge. The adsorption-oxidation mechanism [8] N.I. Khan, G. Owens, D. Bruce, R. Naidu, Human arsenic exposure and risk assessment at the landscape level: a review, Environ. Geochem. Health. 31 (S1) proposed in this study includes a first adsorption of As(III) on the (2009) 143–166, https://doi.org/10.1007/s10653-008-9240-3. surface of the adsorbent, and its oxidation afterwards to As(V) by [9] E. Shaji, M. Santosh, K.V. Sarath, P. Prakash, V. Deepchand, B.V. Divya, Arsenic the OH radicals generated from Fe(III) and the –OH groups pre- contamination of groundwater: a global synopsis with focus on the Indian Peninsula, Geosci. Front. 12 (3) (2021) 101079, https://doi.org/10.1016/j. sent in SPION and sponge adsorbents under neutral conditions. In gsf.2020.08.015. brief, this cube sponge-loaded SPION offers high affinity and good [10] R. Arora, Nano adsorbents for removing the arsenic from waste/ground water adsorption capacity for As(III) together with good diffusion proper- for energy and environment management - a review, Mater. Today Proc. 45 (2021) 4437–4440, https://doi.org/10.1016/j.matpr.2020.12.546. ties and favourable cube-shape which are desirable for industrial [11] H. Zeng, L. Zhai, T. Qiao, Y. Yu, J. Zhang, D. Li, Efficient removal of As(V) from applications. aqueous media by magnetic nanoparticles prepared with Iron-containing water treatment residuals, Sci. Rep. 10 (2020) 9335, https://doi.org/10.1038/ s41598-020-65840-1. CRediT authorship contribution statement [12] S. Tanaka, Y.V. Kaneti, N.L.W. Septiani, S.X. Dou, Y. Bando, M.S.A. Hossain, J. Kim, Y. Yamauchi, A Review on Iron Oxide-Based Nanoarchitectures for Xiang-Yang Lou: Methodology, Formal analysis, Writing – orig- Biomedical, Energy Storage, and Environmental Applications, Small Methods. 3 (5) (2019) 1800512, https://doi.org/10.1002/smtd.v3.510.1002/ inal draft, Writing – review & editing. Roberto Boada: Conceptual- smtd.201800512. ization, Formal analysis, Writing – original draft, Writing – review [13] M.K. Masud, J. Na, M. Younus, M.S.A. Hossain, Y. Bando, M.J.A. Shiddiky, Y. & editing. Laura Simonelli: Methodology. Manuel Valiente: Con- Yamauchi, Superparamagnetic nanoarchitectures for disease-specific biomarker detection, Chem. Soc. Rev. 48 (24) (2019) 5717–5751, https://doi. ceptualization, Methodology, Supervision, Writing – review & edit- org/10.1039/C9CS00174C. ing, Funding acquisition. [14] A. Ali, H. Zafar, M. Zia, I. ul Haq, A.R. Phull, J.S. Ali, A. Hussain, Synthesis, characterization, applications, and challenges of iron oxide nanoparticles, Nanotechnol. Sci. Appl. 9 (2016) 49–67, https://doi.org/10.2147/NSA.S99986. Declaration of Competing Interest [15] F. Gao, Q.i. Qi, X. Wu, J. Yu, J. Yao, Z. Cao, Y. Mi, Q. Cui, Multifunctional poly (quaternary ammonium)/Fe3O4 composite nanogels for integration of The authors declare that they have no known competing finan- antibacterial and degradable magnetic redox-responsive properties, Colloids cial interests or personal relationships that could have appeared Surfaces A Physicochem. Eng. Asp. 615 (2021) 126235, https://doi.org/ 10.1016/j.colsurfa.2021.126235. to influence the work reported in this paper. [16] F. Gao, X. Wu, D. Wu, J. Yu, J. Yao, Q.i. Qi, Z. Cao, Q. Cui, Y. Mi, Preparation of degradable magnetic temperature- and redox-responsive polymeric/Fe3O4 Acknowledgements nanocomposite nanogels in inverse miniemulsions for loading and release of 5-fluorouracil, Colloids Surfaces A Physicochem. Eng. Asp. 587 (2020) 124363, https://doi.org/10.1016/j.colsurfa.2019.124363. We acknowledge CleanWay Environmental Partners, Inc. for [17] H. Su, Z. Ye, N. Hmidi, High-performance iron oxide–graphene oxide kindly supplying the cube-shaped MetalZorbÒ sponge. We nanocomposite adsorbents for arsenic removal, Colloids Surfaces A Physicochem. Eng. Asp. 522 (2017) 161–172, https://doi.org/10.1016/ acknowledge ALBA synchrotron facility for beamtime no. j.colsurfa.2017.02.065. 2018093125 at BL22-CLAESS beamline. This research was finan- [18] Y. Yu, L. Yu, K. Shih, J.P. Chen, Yttrium-doped iron oxide magnetic adsorbent for cially supported by the project CTM2015-65414-C2-1-R from enhancement in arsenic removal and ease in separation after applications, J. Colloid Interface Sci. 521 (2018) 252–260, https://doi.org/10.1016/j. MINECO ministry of Spain. X-Y. Lou acknowledges the China Schol- jcis.2018.02.046. arship Council for his PhD fellowship (No. 201708110179). R. [19] M. Usman, A.I. Belkasmi, I.A. Kastoyiannis, M. Ernst, Pre-deposited dynamic Boada acknowledges funding support from the European Union’s membrane adsorber formed of microscale conventional iron oxide-based adsorbents to remove arsenic from water: application study and mathematical Horizon 2020 research and innovation program under the Marie modeling, J. Chem. Technol. Biotechnol. 96 (6) (2021) 1504–1514, https://doi. Skłodowska-Curie grant agreement No. 665919. org/10.1002/jctb.6728. [20] S.I. Siddiqui, S.A. Chaudhry, Iron oxide and its modified forms as an adsorbent for arsenic removal: a comprehensive recent advancement, Process Saf. Appendix A. Supplementary material Environ. Prot. 111 (2017) 592–626, https://doi.org/10.1016/j. psep.2017.08.009. Supplementary data to this article can be found online at [21] H. Wang, X. Zhao, X. Han, Z. Tang, S. Liu, W. Guo, C. Deng, Q. Guo, H. Wang, F. Wu, X. Meng, J.P. Giesy, Effects of monovalent and divalent metal cations on https://doi.org/10.1016/j.jcis.2022.01.119. the aggregation and suspension of Fe3O4 magnetic nanoparticles in aqueous solution, Sci. Total Environ. 586 (2017) 817–826, https://doi.org/10.1016/j. References scitotenv.2017.02.060. [22] C.-H. Liu, Y.-H. Chuang, T.-Y. Chen, Y. Tian, H. Li, M.-K. Wang, W. Zhang, Mechanism of Arsenic Adsorption on Magnetite Nanoparticles from Water: [1] G.A. Borges, G.M.D. Ferreira, K.P.F. Siqueira, A. Dias, K.O.N. Navarro, S.J.B.e. thermodynamic and Spectroscopic Studies, Environ. Sci. Technol. 49 (13) Silva, G.D. Rodrigues, A.B. Mageste, Adsorption of organic and inorganic arsenic (2015) 7726–7734, https://doi.org/10.1021/acs.est.5b00381. from aqueous solutions using MgAl-LDH with incorporated nitroprusside, J. [23] J. Yao, F. Gao, X. Liang, Y. Li, Y. Mi, Q. Qi, J. Yao, Z. Cao, Efficient preparation of Colloid Interface Sci. 575 (2020) 194–205, https://doi.org/10.1016/j. carboxyl-functionalized magnetic polymer/Fe3O4 nanocomposite particles in jcis.2020.04.078. one-pot miniemulsion systems, Colloids Surfaces A Physicochem. Eng. Asp. [2] V. Reis, A.C. Duarte, Occurrence, distribution, and significance of arsenic 570 (2019) 449–461, https://doi.org/10.1016/j.colsurfa.2019.03.055. speciation, in: Compr. Anal. Chem., Elsevier, 2019: pp. 1–14. https://doi.org/ [24] P. Suresh Kumar, T. Prot, L. Korving, K.J. Keesman, I. Dugulan, M.C.M. van 10.1016/bs.coac.2019.03.006. Loosdrecht, G.J. Witkamp, Effect of pore size distribution on iron oxide coated [3] Z. Yin, J. Lützenkirchen, N. Finck, N. Celaries, K. Dardenne, H.C.B. Hansen, granular activated carbons for phosphate adsorption – Importance of Adsorption of arsenic(V) onto single sheet iron oxide: X-ray absorption fine mesopores, Chem. Eng. J. 326 (2017) 231–239, https://doi.org/10.1016/j. structure and surface complexation, J. Colloid Interface Sci. 554 (2019) 433– cej.2017.05.147. 443, https://doi.org/10.1016/j.jcis.2019.07.024. [25] S. You, S.W. Ho, T. Li, T. Maneerung, C.H. Wang, Techno-economic analysis of [4] M.R. Akanda, I.-S. Kim, D. Ahn, H.-J. Tae, W. Tian, H.-H. Nam, B.-K. Choo, B.-Y. geopolymer production from the coal fly ash with high iron oxide and calcium Park, In Vivo and In Vitro Hepatoprotective Effects of Geranium koreanum 466 Xiang-Yang Lou, R. Boada, L. Simonelli et al. Journal of Colloid and Interface Science 614 (2022) 460–467 oxide contents, J. Hazard. Mater. 361 (2019) 237–244, https://doi.org/10.1016/ [41] Z. Veličković, G.D. Vuković, A.D. Marinković, M.S. Moldovan, A.A. Perić-Grujić, j.jhazmat.2018.08.089. P.S. Uskoković, M.D. Ristić, Adsorption of arsenate on iron(III) oxide coated [26] S. Sharma, A. Hasan, N. Kumar, L.M. Pandey, Removal of methylene blue dye ethylenediamine functionalized multiwall carbon nanotubes, Chem. Eng. J. from aqueous solution using immobilized Agrobacterium fabrum biomass 181–182 (2012) 174–181, https://doi.org/10.1016/j.cej.2011.11.052. along with iron oxide nanoparticles as biosorbent, Environ. Sci. Pollut. Res. 25 [42] B. Moraga, L. Toledo, L. Jelínek, J. Yañez, B.L. Rivas, B.F. Urbano, Copolymer– (22) (2018) 21605–21615, https://doi.org/10.1007/s11356-018-2280-z. hydrous zirconium oxide hybrid microspheres for arsenic sorption, Water Res. [27] M.H. Zeeshan, R.U. Khan, M. Shafiq, A. Sabir, Polyamide intercalated 166 (2019) 115044, https://doi.org/10.1016/j.watres.2019.115044. nanofiltration membrane modified with biofunctionalized core shell [43] A.M.A. Pintor, B.R.C. Vieira, S.C.R. Santos, R.A.R. Boaventura, C.M.S. Botelho, composite for efficient removal of Arsenic and Selenium from wastewater, J. Arsenate and arsenite adsorption onto iron-coated cork granulates, Sci. Total Water Process Eng. 34 (2020) 101175, https://doi.org/10.1016/j. Environ. 642 (2018) 1075–1089, https://doi.org/10.1016/j. jwpe.2020.101175. scitotenv.2018.06.170. [28] Z. Du, M. Ji, R. Li, Enhanced membrane fouling control and trace organic [44] X. Yu, S. Tong, M. Ge, J. Zuo, C. Cao, W. Song, One-step synthesis of magnetic compounds removal during microfiltration by coupling coagulation and composites of cellulose@iron oxide nanoparticles for arsenic removal, J. Mater. adsorption in an electric field, Sci. Total Environ. 795 (2021) 148830, https:// Chem. A. 1 (3) (2013) 959–965, https://doi.org/10.1039/C2TA00315E. doi.org/10.1016/j.scitotenv.2021.148830. [45] A. Sigdel, J. Park, H. Kwak, P.K. Park, Arsenic removal from aqueous solutions [29] D. Morillo, G. Pérez, M. Valiente, Efficient arsenic(V) and arsenic(III) removal by adsorption onto hydrous iron oxide-impregnated alginate beads, J. Ind. Eng. from acidic solutions with Novel Forager Sponge-loaded superparamagnetic Chem. 35 (2016) 277–286, https://doi.org/10.1016/j.jiec.2016.01.005. iron oxide nanoparticles, J. Colloid Interface Sci. 453 (2015) 132–141, https:// [46] X. Song, Y. Wang, L. Zhou, X. Luo, J. Liu, Halloysite nanotubes stabilized doi.org/10.1016/j.jcis.2015.04.048. polyurethane foam carbon coupled with iron oxide for high-efficient and fast [30] A.V. Samrot, H.H. Ali, J. Selvarani A, E. Faradjeva, R. P, P. P, S. Kumar S, treatment of arsenic(III/V) wastewater, Chem. Eng. Res. Des. 165 (2021) 298– Adsorption efficiency of chemically synthesized Superparamagnetic Iron 307, https://doi.org/10.1016/j.cherd.2020.11.001. Oxide Nanoparticles (SPIONs) on crystal violet dye, Curr. Res. Green Sustain. [47] R. Amen, H. Bashir, I. Bibi, S.M. Shaheen, N.K. Niazi, M. Shahid, M.M. Hussain, V. Chem. 4 (2021) 100066, https://doi.org/10.1016/j.crgsc.2021.100066. Antoniadis, M.B. Shakoor, S.G. Al-Solaimani, H. Wang, J. Bundschuh, J. Rinklebe, [31] L. Simonelli, C. Marini, W. Olszewski, M. Ávila Pérez, N. Ramanan, G. Guilera, V. A critical review on arsenic removal from water using biochar-based sorbents: Cuartero, K. Klementiev, Clæss,, The hard X-ray absorption beamline of the The significance of modification and redox reactions, Chem. Eng. J. 396 (2020) ALBA CELLS synchrotron, Cogent Phys. 3 (2016) 1231987, https://doi.org/ 125195, https://doi.org/10.1016/j.cej.2020.125195. 10.1080/23311940.2016.1231987. [48] Y. Wu, R.K. Kukkadapu, K.J.T. Livi, W. Xu, W. Li, D.L. Sparks, Iron and Arsenic [32] B. Ravel, M. Newville, ATHENA, ARTEMIS, HEPHAESTUS: Data analysis for X- Speciation during As(III) Oxidation by Manganese Oxides in the Presence of Fe ray absorption spectroscopy using IFEFFIT, J. Synchrotron Radiat. 12 (4) (2005) (II): Molecular-Level Characterization Using XAFS, Mössbauer, and TEM 537–541, https://doi.org/10.1107/S0909049505012719. Analysis, ACS Earth Sp. Chem. 2 (3) (2018) 256–268, https://doi.org/10.1021/ [33] Y. Xiong, Q. Tong, W. Shan, Z. Xing, Y. Wang, S. Wen, Z. Lou, Arsenic acsearthspacechem.7b0011910.1021/acsearthspacechem.7b00119.s001. transformation and adsorption by iron hydroxide/manganese dioxide doped [49] G. Ona-Nguema, G. Morin, F. Juillot, G. Calas, G.E. Brown, EXAFS Analysis of straw activated carbon, Appl. Surf. Sci. 416 (2017) 618–627, https://doi.org/ Arsenite Adsorption onto Two-Line Ferrihydrite, Hematite, Goethite, and 10.1016/j.apsusc.2017.04.145. Lepidocrocite, Environ. Sci. Technol. 39 (23) (2005) 9147–9155, https://doi. [34] J.O. De Marques Neto, C.R. Bellato, J.L. Milagres, K.D. Pessoa, E.S. De Alvarenga, org/10.1021/es050889p10.1021/es050889p.s001. Preparation and evaluation of chitosan beads immobilized with iron(III) for [50] X. Dong, L.Q. Ma, J. Gress, W. Harris, Y. Li, Enhanced Cr(VI) reduction and As(III) the removal of As(III) and As(V) from water, J. Braz. Chem. Soc. 24 (2013) 121– oxidation in ice phase: Important role of dissolved organic matter from 132, https://doi.org/10.1590/S0103-50532013000100017. biochar, J. Hazard. Mater. 267 (2014) 62–70, https://doi.org/10.1016/j. [35] Y. Liu, Y. Xiong, P. Xu, Y.a. Pang, C. Du, Enhancement of Pb (II) adsorption by jhazmat.2013.12.027. boron doped ordered mesoporous carbon: Isotherm and kinetics modeling, Sci. [51] P. Pe˛dziwiatr, F. Mikołajczyk, D. Zawadzki, K. Mikołajczyk, A. Bedka, Total Environ. 708 (2020) 134918, https://doi.org/10.1016/j. Decomposition of hydrogen peroxide - kinetics and review of chosen scitotenv.2019.134918. catalysts, Acta Innov. (26) (2018) 45–52, https://doi.org/10.32933/ [36] H.N. Tran, S.-J. You, A. Hosseini-Bandegharaei, H.-P. Chao, Mistakes and ActaInnovations10.32933/10.32933/ActaInnovations.2610.32933/ inconsistencies regarding adsorption of contaminants from aqueous solutions: ActaInnovations.26.5. a critical review, Water Res. 120 (2017) 88–116, https://doi.org/10.1016/j. [52] B. Chen, Z. Zhu, J. Ma, M. Yang, J. Hong, X. Hu, Y. Qiu, J. Chen, One-pot, solid- watres.2017.04.014. phase synthesis of magnetic multiwalled carbon nanotube/iron oxide [37] Y. Tong, P.J. McNamara, B.K. Mayer, Adsorption of organic micropollutants composites and their application in arsenic removal, J. Colloid Interface Sci. onto biochar: a review of relevant kinetics, mechanisms and equilibrium, 434 (2014) 9–17, https://doi.org/10.1016/j.jcis.2014.07.046. Environ. Sci. Water Res. Technol. 5 (5) (2019) 821–838, https://doi.org/ [53] J.C. Bullen, J.P.L. Kenney, S. Fearn, A. Kafizas, S. Skinner, D.J. Weiss, Improved 10.1039/C8EW00938D. accuracy in multicomponent surface complexation models using surface- [38] B. Adane, K. Siraj, N. Meka, Kinetic, equilibrium and thermodynamic study of sensitive analytical techniques: adsorption of arsenic onto a TiO2/Fe2O3 2-chlorophenol adsorption onto Ricinus communis pericarp activated carbon multifunctional sorbent, J. Colloid Interface Sci. 580 (2020) 834–849, https:// from aqueous solutions, Green Chem. Lett. Rev. 8 (3-4) (2015) 1–12, https:// doi.org/10.1016/j.jcis.2020.06.119. doi.org/10.1080/17518253.2015.1065348. [54] J. Alchouron, C. Navarathna, P.M. Rodrigo, A. Snyder, H.D. Chludil, A.S. Vega, G. [39] E.C. Lima, A. Hosseini-Bandegharaei, J.C. Moreno-Piraján, I. Anastopoulos, A Bosi, F. Perez, D. Mohan, C.U. Pittman Jr., T.E. Mlsna, Household arsenic critical review of the estimation of the thermodynamic parameters on contaminated water treatment employing iron oxide/bamboo biochar adsorption equilibria. Wrong use of equilibrium constant in the Van’t Hoof composite: an approach to technology transfer, J. Colloid Interface Sci. 587 equation for calculation of thermodynamic parameters of adsorption, J. Mol. (2021) 767–779, https://doi.org/10.1016/j.jcis.2020.11.036. Liq. 273 (2019) 425–434, https://doi.org/10.1016/j.molliq.2018.10.048. [55] Y. Xu, X. Xie, Y.u. Feng, M.A. Ashraf, YingYing Liu, C. Su, K. Qian, P. Liu, As(III) [40] J. Gimenez, M. Martinez, J. Depablo, M. Rovira, L. Duro, Arsenic sorption onto and As(V) removal mechanisms by Fe-modified biochar characterized using natural hematite, magnetite, and goethite, J. Hazard. Mater. 141 (3) (2007) synchrotron-based X-ray absorption spectroscopy and confocal micro-X-ray 575–580, https://doi.org/10.1016/j.jhazmat.2006.07.020. fluorescence imaging, Bioresour. Technol. 304 (2020) 122978, https://doi.org/ 10.1016/j.biortech.2020.122978. 467