Synthesis of ultra-large ZrO2 nanosheets as novel adsorbents for fast and efficient removal of As(III) from aqueous solutions

Coating zirconium oxide-nanocomposite with humic acid for recovery of mercury and chromium in hazardous waste of chemical oxygen demand test

Hazardous waste of chemical oxygen demand (COD) test (HW_COD) is one of the most common laboratory wastewaters, containing large amounts of H₂SO₄ and highly toxic Cr³⁺ and Hg²⁺. Current treatment methods suffered from incomplete removal of Cr³⁺ and high-cost. Herein, a humic acid-coated zirconium oxide-resin nanocomposite (HA-HZO-201) was fabricated for efficient recovery of Cr³⁺ and Hg²⁺ in HW_COD. The synthesized HA-HZO-201 shows excellent tolerance to wide pH range (1-5) and high salinity (3.5 mol/L NaCl), as well as adsorption capacity for Cr³⁺ (37.5 mg/g) and Hg²⁺ (121.3 mg/g). After treating with HA-HZO-201 by using a fixed-bed adsorption procedure, the final Cr³⁺ and Hg²⁺ concentrations in HW_COD decreased to 0.28 and 0.02 mg/L, respectively. In addition, the HA-HZO-201 can be regenerated by desorption and recovery of Cr³⁺ and Hg²⁺ using HNO₃ and thiourea as eluents, respectively. After 5 cycles of adsorption/desorption, the removal efficiencies still reach up to 86.0% for Cr³⁺ and 89.7% for Hg²⁺, indicating an excellent regeneration of HA-HZO-201. We hope this work open new opportunities for treatment of HW_COD with high-efficiency and low-cost.

Interface catalytic regulation via electron rearrangement and hydroxyl radicals triggered by oxygen vacancies and heavy metal ions

Although the enhanced intrinsic activities of some nano-metal oxides are obtained by manufacturing oxygen vacancies (OVs), the effect of multiple roles of OVs is ambiguous. Herein, an interface catalytic regulation via electron rearrangement and hydroxyl radicals (˙OH) was proposed with the designed ZrO₂ hollow sphere rich in OVs (V_o-rich ZrO₂). Surprisingly, it was shown that the catalytic ability of V_o-rich ZrO₂ was 9.9 times higher than that of ZrO₂ with little OVs in electrochemical catalytic reduction of Pb(ii). It was found that the generation of Zr²⁺ and Zr³⁺ caused by OVs results in the rearrangement of abundant free electrons to facilitate the catalytic reaction rates. The longer bond length between V_o-rich ZrO₂ and reactants, and the lower adsorption energy are beneficial for reactants to desorb, improving the conversion rates. Besides, the produced ˙OH were captured which were induced by OVs and trace divalent heavy metal ions in in situ electron paramagnetic resonance (EPR) experiments, contributing to lowering the energy barriers. This study not only revealed the enhanced interface catalytic effect of electron rearrangement and generated ˙OH triggered by OVs, but also provided unique insights into interface catalytic regulation on nano-metal oxides simulated by OVs.

Nanocomposites of immobilized nano-zirconia on low-cost activated carbon derived from hazelnut shell for enhanced removal of 3-Nitro-4-Hydroxy-Phenylarsonic acid from water

3-Nitro-4-hydroxy-phenylarsonic acid (NHPA) as a veterinary drug can degraded into highly toxic inorganic arsenic and will be harmful to environment and food safety. Nanocomposites for the uptake of NHPA were obtained by efficiently immobilizing the nano-sized zirconium oxide onto hazelnut shell-based activated carbon using pyrolysis method. We found that the pyrolysis temperature played a crucial role in the adsorptive performances of the nanocomposites. The prepared nanocomposite at pyrolysis temperature of 600 °C with a mass ratio of ZrOCl₂/activated carbon of 1:3 exhibited a fast adsorption equilibrium for NHPA within 5 min, excellent adsorption capacity of 825.7 mg g^-1 and the higher adsorption capacity with the increase in temperature from 20 to 45 °C across a pH range of 4-6. 90% of the NHPA uptake was sustained in the NaNO₃ solution of 0.7 mol L^-1. The adsorption data were well simulated by the Langmuir and pseudo-second order equations. Thermodynamic parameters suggested that the uptake of the NHPA occurred spontaneously (ΔG⁰<0) with an endothermic characteristic (ΔH⁰>0). A synergetic effect of electrostatic attraction, As-O-Zr surface coordination and π-π interaction is the main adsorption mechanism of the nanocomposites for the removal of the NHPA.

Recent advances in application of iron-manganese oxide nanomaterials for removal of heavy metals in the aquatic environment

Heavy metal pollution has a serious negative impact on the ecological environment and human health due to its toxicity, persistence, and non-biodegradable properties. Among the technologies applied in heavy metals removal, adsorption has been widely used as the most promising method because of its simple operation, high removal efficiency, strong applicability, and low cost. Iron-manganese oxide nanomaterials, as an effective absorbent, have attracted wide attention due to their simple preparation, wide material sources, and lower ecological impact. So far, no quantitative investigation has been conducted on the preparation and application of iron-manganese oxide nanomaterials in heavy metals removal. This review discussed the preparation methods and characteristics of iron‑manganese oxide nanomaterials over the past decade and provided some basic information for the improvement of preparation methods. The physicochemical properties of iron‑manganese oxide nanomaterials and environmental conditions are regarded as important factors that affect the removal efficiency of heavy metals. In addition, the removal mechanisms of heavy metals in aqueous solution with iron‑manganese oxide nanomaterials were mainly included redox, complex precipitation, electrostatic attraction, and ion exchange. The reusability and practicability in actual wastewater treatment of 3nganese oxide nanomaterials were further discussed. Several key problems still need to be solved in the existing progress, such as improving the ability and stability of the iron‑manganese oxide nanomaterials to remove heavy metals from actual wastewater. In conclusion, this review provides a future direction for the application of iron‑manganese oxide nanomaterials for heavy metals removal and even in the large-scale treatment of actual wastewater.

Magnetic adsorbent developed with alkali-thermal pretreated biogas slurry solids for the removal of heavy metals: optimization, kinetic, and equilibrium study

Discharge of effluents containing heavy metal without adequate treatment causes contamination of water resources and creates environmental and health issues. Adsorption could be applied to remediate heavy metals from wastewater effectively. In this study, a low-cost adsorbent was prepared by magnetic modification of pretreated biogas slurry solids (BSS) to remove heavy metals such as Cu²⁺, Cd²⁺, and Pb²⁺. The temperature (423 K) and time (1.5 h) of pretreatment, the BSS to KOH ratio (1:10 w/v), and the ratio of magnetic iron nanoparticle (MIN) to pretreated BSS (PSS) (1:2 w/w) were optimized for the preparation of adsorbent. The magnetically modified pretreated biogas slurry solid (MMPSS) adsorbent was characterized by BET isotherm, FTIR, XRD, FESEM, VSM, and EDX analysis. MMPSS attained equilibrium at 60 min and showed an adsorption capacity of 26.84 mg/g, 24.79 mg/g, and 23.86 mg/g with removal percentages 89.46%, 82.63%, and 79.54% for Cu²⁺, Cd²⁺, and Pb²⁺, respectively, at 310 K and pH 6 with an initial concentration of 150 mg/L. The adsorption process followed a pseudo second-order model with an R² value above 0.9 for all metals with a well-approaching equilibrium pattern. The good fit of experimental data by the Langmuir isotherm model implied monolayer adsorption. The metal ions adsorbed onto MMPSS were able to desorb effectively in the presence of HCl and retained 83.01%, 84.66%, and 81.83% of the initial adsorption capacity for Cu²⁺, Cd²⁺, and Pb²⁺ respectively after 5 consecutive cycles.

UiO-66(Zr)-derived t-zirconia with abundant lattice defect for remarkably enhanced arsenic removal

Zirconium oxide (ZrO₂) exhibits great potential in the remediation of arsenic-polluted water. In this study, tetragonal zirconium oxide (t-ZrO₂) with high lattice defects was facilely fabricated by regulating the Zr-metal-organic framework (MOF) (UiO-66) with sodium acetate modulator and examined to adsorb arsenic from water. Benefitting from the synergistic effects of mesopores structure and lattice defect, t-ZrO₂ exhibited ultrahigh adsorption capacity and faster kinetics towards both arsenate (As(V)) and arsenite (As(III)). The Langmuir adsorption capacity for As(V) and As(III) of 147.5 mg g^-1 and 352.1 mg g^-1 on t-ZrO₂ in exothermic process, respectively, significantly outperforming reported counterparts in literature (generally ≤100 mg g^-1). The faster adsorption kinetic of both As(III) and As(V) on t-ZrO₂ is defined favorably by the pseudo-second-order model over a wide pH (3-11). Furthermore, arsenic is mainly captured by t-ZrO₂ via forming Zr-O-As bonds through occupying coordinatively unsaturated zirconium atoms adsorption sites revealed by the X-ray photoelectron spectroscopy (XPS) spectrum and Fourier-transformed infrared (FTIR) spectra analysis. This study offers a new strategy for designing ultrahigh performance Zr-MOF-derived adsorbents for capturing arsenic.

Mesoporous cerium oxide-anchored magnetic polyhedrons derived from MIL-100(Fe) for enhanced removal of arsenite from aqueous solution

Efficient elimination of As(III) from drinking water and wastewater has been a challenge because of its neutral molecular form. To address this problem, a novel nanocomposite, mesoporous cerium oxide-anchored magnetic polyhedrons derived from MIL-100(Fe) was fabricated via a strategy combining impregnation and calcination. The resultant products (denoted as Fe₂O₃/CeO₂-t) exhibited a unique octahedral nanostructure decorated by mesoporous cerium oxide. Surface modification of CeO₂ enhanced As(III) removal in comparison to unmodified Fe₂O₃. Particularly, Fe₂O₃/CeO₂-4 h can reduce As(III) concentration from 180 to 10 µg/L within 20 min, which was almost 9 times faster than unmodified Fe₂O₃. The adsorption behavior conformed to the pseudo-second-order kinetic model (R² = 0.9908) and the Freundlich isotherm model (R² = 0.9943). The maximum adsorption capacity of As(III) by Fe₂O₃/CeO₂-4 h was 68.25 mg/g, higher than those reported for similar adsorbents. Its enhanced removal mechanism can be attributed mainly to the mesoporous characteristics and oxidization ability of surface ceria. The composite can be separated from water by external magnets and easily regenerated. This study may offer a clue to the design of metal-organic framework-based composites as an alternative adsorbent for arsenite cleanup.

Magnetic zeolitic imidazolate frameworks composite as an efficient adsorbent for arsenic removal from aqueous solution

In this study, magnetic zeolitic imidazolate frameworks (ZIF-8) was prepared by a one-step method, where its evolution involved the coprecipitation reactions concomitant with the self-assembly reactions. Structural characterizations indicated that magnetic ZIF-8 showed irregular polyhedral morphology with a large specific surface area (696.5 m²/g) and saturation magnetization (4.31 emu/g). The as-prepared magnetic ZIF-8 enhanced the adsorption performance of As(III) and As(V), compared with bare Fe₃O₄. The pseudo second-order kinetic model (R² = 0.9627 and 0.9893 for As(III) and As(V), respectively) and the Langmuir model (R² = 0.9441 for As(III) and 0.9851 for As(V)) can fit the adsorption process well, confirming the nature of single-layer homogeneous chemisorption. The adsorption capacity was 30.87 and 17.51 mg/g, and their corresponding values of PC were 2.664 and 1.286 L/g, for As(III) and As(V), respectively. Solution pH showed an adverse effect on As(V) adsorption whereas no obvious effect on As(III). The ionic strength and coexisting ions had not obvious influence on adsorption of As(III) and As(V). The adsorption mechanism was explored and discussed based on the detailed spectroscopy analysis. This adsorbent can be recovered magnetically after use, which is promising for the practical application.

Adsorptive Removal of Cd, Cu, Ni and Mn from Environmental Samples Using Fe3O4-Zro2@APS Nanocomposite: Kinetic and Equilibrium Isotherm Studies

In this study, Fe₃O₄-ZrO₂ functionalized with 3-aminopropyltriethoxysilane (Fe₃O₄-ZrO₂@APS) nanocomposite was investigated as a nanoadsorbent for the removal of Cd(II), Cu(II), Mn (II) and Ni(II) ions from aqueous solution and real samples in batch mode systems. The prepared magnetic nanomaterials were characterized using X-ray powder diffraction (XRD), scanning electron microscopy/energy dispersion x-ray (SEM/EDX) Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Factors (such as adsorbent dose and sample pH) affecting the adsorption behavior of the removal process were studied using the response surface methodology. Under optimized condition, equilibrium data obtained were fitted into the Langmuir and Freundlich isotherms and the data fitted well with Langmuir isotherms. Langmuir adsorption capacities (mg/g) were found to be 113, 111, 128, and 123 mg/g for Cd, Cu, Ni and Mn, respectively. In addition, the adsorption kinetics was analyzed using five kinetic models, pseudo-first order, pseudo-second order, intraparticle diffusion and Boyd models. The adsorbent was successfully applied for removal of Cd(II), Cu(II), Mn (II) and Ni(II) ions in wastewater samples.

Experimental and statistical analysis of As(III) adsorption from contaminated water using activated red mud doped calcium-alginate beads

Arsenic present in water bodies causes devastating effects on aquatic organisms and indirectly poses a hazardous threat to human existence. There is an urgent need to develop potential and convincing technologies to troubleshoot this problem. In the present study, an adsorbent has been prepared using the waste red mud from hazardous aluminium industry and doping it with calcium-alginate beads (ARMCB) for the effective removal of As(III) from wastewater. The concentration of As(III) was reduced from 0.101 mg/L to 0.008 mg/L after adsorption which effectively met the economic and environmental conditions imposed by WHO (>0.01 mg/L). Further, the statistical Response Surface Methodology (RSM) is adopted to analyze the combined effects of four operational parameters namely: pH, sorbent dosage, contact time and initial concentration on the adsorption of As(III) from the synthetic contaminated water samples. A high correlation coefficient (R2) value of 0.9672 projected by ANOVA confirmed the satisfactory regression of the developed model. The maximum adsorption capacity is found to be 1.807 mg/g at optimum operating conditions. The surface characterization of the adsorbent before and after adsorption by SEM, EDX, XRD, and FTIR confirms the potentiality of the adsorbent towards As(III) ions. Thermodynamic, adsorption isotherms and kinetic analysis respectively projected the endothermic Langmuir model adsorption of As(III) and the pseudo-second-order rate kinetics of the sorption mechanism. The current study aids the implementation of the developed robust technique for the successful removal of As(III) from industrial and domestic polluted water samples.

Iron oxides decorated graphene oxide/chitosan composite beads for enhanced Cr(VI) removal from aqueous solution

This study is the first to evaluate the effects of Iron oxides (FeO_x) species and their decoration on graphene oxide/chitosan (GO/CS) composites for Cr(VI) removal and the possibility of Fe secondary pollution. Results show that Fe(III) is a better decoration material than Fe(II) and decoration through immersion-evaporation shows a higher adsorption capacity of Cr(VI) (Q_e) than co-precipitation. Fe₂O₃-GO/CS as the only eco-friendly composite for enhanced Cr(VI) removal is further used for batch adsorption experiments, characterization, kinetics, isotherms, and thermodynamic studies. It is found that Cr(VI) removal mainly includes electrostatic attraction between Cr(VI) oxyanions and surface -NH₃⁺ and -OH₂⁺, and the adsorbed Cr(VI) partially reduces to Cr(III). Q_e increases with the increasing initial Cr(VI) concentration, contact time, and temperature, while decreases with the increasing pH and mass and volume ratio (m/v). The coexisting ions (Cl^-, NO₃^-, SO₄^2-, PO₄^3-, As, Fe, and Pb) can cause an obvious decrease of Q_e. The removal efficiency (R_e) and Q_e are 94.3% and 83.8 mg/g, respectively under the optimal conditions. After five times of regeneration, R_e is still as high as 84% and Q_e drops about 2.6%. Cr(VI) adsorption is spontaneous and endothermic, which is best fitted with the Sips model, and the fitted maximum Q_e is 131.33 mg/g.

Agro-Waste Derived Biomass Impregnated with TiO2 as a Potential Adsorbent for Removal of As(III) from Water

A novel type of adsorbent, TiO2 impregnated pomegranate peels (PP@TiO2) was successfully synthesized and its efficacy was investigated based on the removal of As(III) from water. The adsorbent was characterized using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectrometer (EDS), X-ray Diffraction (XRD) analysis, and Fourier Transform Infrared (FTIR) Spectroscopy, to evaluate its morphology, elemental analysis, crystallinity, and functional groups, respectively. Batch experiments were conducted on PP@TiO2 for As(III) adsorption to assess the adsorption isotherm, effect of pH, and adsorption kinetics. Characterization data suggested that TiO2 was successfully impregnated on the biomass substrate. The equilibrium data better fitted to the Langmuir isotherm model having a maximum adsorption capacity of 76.92 mg/g and better distribution coefficients (KD) in the order of ~103 mL/g. The highest percentage of adsorption was found at neutral pH. The adsorption kinetics followed the pseudo-2nd-order model. X-ray Photoelectron Spectroscopy (XPS) of the adsorption product exhibited that arsenic was present as As(III) and partially oxidized to As(V). PP@TiO2 can work effectively in the presence of coexisting anions and could be regenerated and reused. Overall, these findings suggested that the as-prepared PP@TiO2 could provide a better and efficient alternative for the synergistic removal of As(III) from water.

Cu(II)-Fe(III) oxide doped anion exchangers - Multifunctional composites for arsenite removal from water via As(III) adsorption and oxidation

The aim of the present study was to investigate As(III) oxidation and adsorption on the surface of hybrid anion exchangers containing Cu(II)-Fe(III) binary oxide deposited in their porous structure with the same Cu:Fe ratio of 1:2 but with different amounts and distribution of inorganic deposit within polymeric beads. The equilibrium studies confirmed high adsorption capacity of the best hybrid polymer: 94.4 mg As/g. Moreover, the adsorption was effective over a wide pH range, selective in the presence of interfering ions, and the material was effectively regenerated. The performance of the hybrid polymer was also confirmed in the column process which enabled both As(III) and As(V) concentrations to be lowered from 500 μg/L to below 10.0 μg/L in a solution with a composition similar to natural groundwater. The breakthrough point of the bed was reached after the solution amounting to 1833 bed volumes passed through the column. Desorbed As speciation, FTIR and XPS studies showed that As(III) was mainly adsorbed on the surface of Cu-Fe oxides followed by its oxidation to As(V). In the oxidation reaction metal oxides acted as catalysts and adsorbents, while the oxidant was probably oxygen dissolved in solution.

Mesoporous zirconia nanostructures (MZN) for adsorption of As(III) and As(V) from aqueous solutions

Mesoporous zirconia nanostructures (MZN) were synthesized by hydrothermal method to efficiently remove highly mobile and toxic arsenite (As(III)) and arsenate (As(V)) from aqueous solutions. The as-synthesized MZN were characterized by Brunauer-Emmett-Teller (BET), X-Ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM), and Energy-dispersive X-ray spectroscopy (EDX) techniques. The batch adsorption experimental results showed that the As(III) and As(V) removal capacities of the MZN were 105.03 and 110.29 mg/g, respectively, under neutral pH conditions, which were better than many recently reported adsorbents. The adsorption behavior of As(III) and As(V) on the MZN could be well described by pseudo-second-order and Langmuir isotherms models. Moreover, As(III) and As(V) adsorption on the MZN was spontaneous and endothermic. Some of the common co-existing ions had slightly affected the arsenic removal proficiency of MZN. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to investigate the adsorption mechanism of As(III) and As(V) on the as-synthesized MZN. The as-synthesized MZN demonstrated quite fast and good treatment of simulated real arsenic (As(III,V)) contaminated water. This study suggested that the as-synthesized MZN are potential candidate for practical applications of As(III) and As(V) removal from the aqueous solutions.