Formation Of Inner-sphere Complexes Research Articles

Transferring red mud to efficient adsorbent for the adsorption and immobilization of Ni(Ⅱ) from aqueous solution

Red mud, a solid waste produced in large quantities, possesses a high specific surface area and is rich in metal oxides, making it a promising material for adsorbent preparation. However, its practical application is constrained by its relatively low adsorption capacity and the potential environmental risks it poses. This study focused on the preparation of modified red mud (MRM) with enhanced adsorption performance for Ni2+ using a hydrothermal method involving sodium hydroxide and colloidal silica. The maximum adsorption capacity of MRM for Ni2+ reached 8.22 mmol·g–1, a substantial improvement compared to raw red mud (0.28 mmol·g–1) and sulfuric acid-activated red mud (0.46 mmol·g–1). The pseudo-second-order kinetic and Langmuir isotherm models accurately described the monolayer chemical adsorption process of Ni2+ on MRM. Additionally, leaching tests with simulated rainwater demonstrated that Ni-loaded MRM exhibited high stability, suggesting its potential for safe stockpiling or repurposing, such as in construction materials. Sequential extraction, XRD, FT-IR, and XPS results revealed that cation exchange was the primary mechanism in the adsorption process, with Ni2+ being immobilized within the zeolite framework structure of MRM, contributing to its strong adsorption stability. Inner-sphere complex formation also played a role in Ni2+ adsorption. In conclusion, this method offers an effective approach to both red mud utilization and heavy metal removal from wastewater, presenting a practical solution for waste management through resource recovery and environmental remediation.

Interception of internal phosphorus release from sediments by lanthanum-modified shrimp shell biochar in two application modes

Lanthanum (La)-modified biochar has been widely investigated as a phosphate adsorbent material. However, its effectiveness and mechanism as an amendment material to manage sediment internal phosphorus (P) release under anoxic conditions is still unclear. Thus, a lanthanum carbonate-modified shrimp shell biochar (LBC-1) was synthesized for controlling sediment P release, and the efficacy, mechanism, and sediment microbial community impact of LBC-1 under two application modes (addition and capping) were investigated. The maximum adsorption capacity of LBC-1 for phosphate was 79.5 mg/g, superior to most La-modified biochar materials. The generation of LaPO4 and Ca5(PO4)3(OH) precipitates and the formation of inner-sphere complexes were the main adsorption mechanisms of LBC-1 for phosphate. Both the LBC-1 addition and capping treatments successfully blocked sediment P release under anoxic conditions, with the removal efficiencies of DGT-labile P in the overlying water being 97.7–99.7% and 97.5–99.5%, respectively. The conversion of the mobile P forms to the stable HCl-P form in sediments played an important role in the interception of internal P release by the LBC-1 addition treatment. Furthermore, the LBC-1 addition treatment also prevented internal P release by effectively adsorbing DGT-labile P in the interstitial water due to the excellent P adsorption capacity of LBC-1. However, the prevention of P release from sediments by the LBC-1 capping treatment was mainly attributed to the efficient adsorption of DGT-labile P by LBC-1 at the sediment/overlying water interface. The release of P driven by sulfate-reducing bacteria (SRB) was a key mechanism for the migration of P from sediment to interstitial water. The LBC-1 addition treatment reduced the relative abundance of SRB in the surface sediment and might inhibit the release of sediment P into the interstitial water, whereas the LBC-1 capping treatment had little effect on the relative abundance of SRB. In practice, the LBC-1 capping was easier to manipulate than the LBC-1 addition. These findings confirmed that sediment remediation using the LBC-1 capping treatment has great potential to manage internal P loading in eutrophic water bodies.

Application of modified clays in the removal of phosphates and E. coli from aqueous solution

The presence of microorganisms and inorganic pollutants in water bodies results in adverse effects on nature as well as human health. In this study, clay-based adsorbents were used for the removal of phosphates and Escherichia coli bacteria. Two samples, Na-Zr-50-2.5 and Na-Zr-50-5, were prepared using 2.5 and 5 mmol of zirconium per gram of clay. The former material has shown better Langmuir phosphate adsorption capacity (∼11.5 mg P/g) at pH 4. Chitosan modification was applied to Na-Zr-50-2.5 to improve its performance at higher pH. Post modification, the maximum adsorption attained at pH 4 was 14.5 mg P/g, and it improved from 8.3 to 11.8 mg P/g at pH 7. The possible major governing mechanism responsible for the adsorption of phosphates was the formation of inner-sphere complexes. Application of Na-Zr-50-2.5 was also explored for removing E. coli cells from aqueous saline solution. The E. coli removal efficiency of this sample was found to be 62.64 %. This study reveals that modified clays effectively reduce the phosphate and E. coli levels in aqueous solution and can be proved as environment-friendly, low-budget adsorbent materials in wastewater treatment.

Investigating the sorption behavior of selenite on commercial partially oxidized magnetite nanopowder under aerobic conditions: Characterization and mechanisms

Selenium, which belongs to essential elements, has a narrow margin between necessity and toxicity. Anthropogenic activities may lead to its elevated concentrations in aquatic ecosystems, particularly in the undesirable form of toxic selenite, due to its high environmental mobility. Hence, it is imperative to devise effective technologies to limit its potential migration through the environment. Therefore, the development and evaluation of new adsorbents for its effective removal from selenium-contaminated waters are crucial for both human health and environmental stability in affected areas. Specifically, magnetite-based nanomaterials showed promise as sorbents due to their capacity to immobile contaminants through reductive transformation or adsorption, but there is a lack of comprehensive understanding regarding the sorption mechanisms and the factors influencing the efficiency of this process. A deeper understanding of these factors is crucial for developing sustainable and efficient water treatment strategies. This study focuses on magnetite nanopowder’s sorptive properties, examining critical factors such as pH, ionic strength, and competing anions that affect selenite removal. Sorption kinetics revealed an initial rapid selenite removal followed by a slower, time-dependent phase, suggesting a complex sorption mechanism. Chemisorption was considered the primary sorptive interaction, with diffusion playing a minor role, and was best described by the pseudo-second order kinetic model. Notably, pH significantly affected sorption efficiency and the suggested sorptive mechanism. Acidic conditions favored selenite removal due to formation of inner-sphere complexes, while alkaline conditions reduced efficiency due to repulsive interactions. Equilibrium sorption data were best fitted by the Langmuir model, with maximum sorption at pH 3, indicating that acidic conditions favor selenite removal. X-ray photoelectron spectroscopy (XPS) analysis ruled out the formation of reduced selenium compounds on the magnetite nanopowder surfaces. Additionally, Mössbauer spectrometry revealed that the nanopowder is not homogeneous and contains both magnetite and maghemite phases. Ionic strength and co-occurring ions showed minimal chloride impact but significant phosphate competitiveness due to its affinity for iron oxides. In conclusion, this study sheds light on the complex selenite sorptive interactions with magnetite nanopowder, emphasizing the dominance of chemisorption, especially in acidic solutions.

Nanosized lanthanum peroxide–loaded biochar composites for simple and effective glyphosate removal from wastewater: Behavior and mechanisms

The extensive use of glyphosate-based herbicides and its high solubility in water have led to its accumulation in aquatic environments, posing a risk to the ecological environment and human health. Therefore, an effective method for removing glyphosate from wastewater is urgently needed. Herein, a novel nanosized lanthanum peroxide–loaded biochar composite (n-LBC) was prepared using a simple precipitation method, in which biochar served as a dispersant and catalyst to improve the oxidation ability of nanosized lanthanum peroxide. Compared with other common metal peroxide systems, n-LBC exhibited better oxidation ability and achieved a glyphosate removal efficiency of 99.6%. Moreover, n-LBC retained the self-buffering effect of lanthanum peroxide and thus remained effective over a wide pH range, overcoming the problem of pH elevation observed in other metal peroxide systems. The mechanism for glyphosate removal was found to be a combined process of electrostatic attraction, oxidation, and inner-sphere complex formation. Most glyphosate could be oxidized to H2PO 4− by breaking the C–N bonds, and H2PO4− could be attracted to the material surface simultaneously by electrostatic attraction, forming La–O–P inner-sphere complexes. Thus, n-LBC is a simple and highly effective material for glyphosate removal.

Spectroscopic and Microscopic Characterization of Microbial Biofouling on Aircraft Fuel Tanks.

Avoiding microbial contamination and biofilm formation on the surfaces of aircraft fuel tanks is a major challenge in the aviation industry. The inevitable presence of water in fuel systems and nutrients provided by the fuel makes an ideal environment for bacteria, fungi, and yeast to grow. Understanding how microbes grow on different fuel tank materials is the first step to control biofilm formation in aviation fuel systems. In this study, biofilms of Pseudomonas putida, a model Gram-negative bacterium previously found in aircraft fuel tanks, were characterized on aluminum 7075-T6 surfaces, which is an alloy used by the aviation industry due to favorable properties including high strength and fatigue resistance. Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX) showed that extracellular polymeric substances (EPS) produced by P. putida were important components of biofilms with a likely role in biofilm stability and adhesion to the surfaces. EDX analysis showed that the proportion of phosphorus with respect to nitrogen is higher in the EPS than in the bacterial cells. Additionally, different morphologies in biofilm formation were observed in the fuel phase compared to the water phase. Micro-Fourier transform infrared spectroscopy (micro-FTIR) analysis suggested that phosphoryl and carboxyl functional groups are fundamental for the irreversible attachment between the EPS of bacteria and the aluminum surface, by the formation of hydrogen bonds and inner-sphere complexes between the macromolecules and the aluminum surface. Based on the hypothesis that nucleic acids (particularly DNA) are an important component of EPS in P. putida biofilms, the impact of degrading extracellular DNA was tested. Treatment with the enzyme DNase I affected both water and fuel phase biofilms─with the cell structure disrupted in the aqueous phase, but cells remained attached to the aluminum coupons.

Removal of phosphorus by modified bentonite:polyvinylidene fluoride membrane-study of adsorption performance and mechanism.

Enhanced phosphorus management, geared towards sustainability, is imperative due to its indispensability for all life forms and its close association with water bodies' eutrophication, primarily stemming from anthropogenic activities. In response to this concern, innovative technologies rooted in the circular economy are emerging, to remove and recover this vital nutrient to global food production. This research undertakes an evaluation of the dead-end filtration performance of a mixed matrix membrane composed of modified bentonite (MB) and polyvinylidene fluoride (PVDF) for efficient phosphorus removal from water media. The MB:PVDF membrane exhibited higher permeability and surface roughness compared to the pristine membrane, showcasing an adsorption capacity (Q) of 23.2 mgP·m-2. Increasing the adsorbent concentration resulted in a higher removal capacity (from 16.9 to 23.2 mgP·m-2) and increased solution flux (from 0.5 to 16.5 L·m-2·h-1) through the membrane. The initial phosphorus concentration demonstrates a positive correlation with the adsorption capacity of the material, while the system pressure positively influences the observed flux. Conversely, the presence of humic acid exerts an adverse impact on both factors. Additionally, the primary mechanism involved in the adsorption process is identified as the formation of inner-sphere complexes.

Construction of 3D network aluminum sludge-based hydrogel beads: combination of macroization, amino functionalization, and resource utilization.

An aluminum sludge-based composite material was constructed against the problems of phosphorus pollution and the waste of aluminum sludge resources. Utilizing metal Ce doping and hydrogel microbeads with pore preparation, the adsorption performance of the original sludge was improved. Meanwhile, the macroscopic body was constructed, and on this basis, polyethyleneimine (PEI) was introduced to complete the amino functionalization further to enhance the adsorption of phosphorus by the adsorbent, and NH-CeAIS-10 microbeads were successfully prepared. In adsorption, microbeads with larger specific surface area and richer functional groups are better choice compared to original sludge. The results of SEM, BET, FT-IR, and XPS analyses indicate that the adsorption of phosphorus by the microbeads is mainly achieved through electrostatic interactions, ligand exchange, and the formation of inner-sphere complexes. According to the Langmuir model, the maximum phosphorus adsorption capacity of NH-CeAIS-10 was 29.56mgg-1, which was four times higher compared to native aluminum sludge. This also confirms the significant enhancement of phosphorus adsorption through the modification of aluminum sludge. Besides, in dynamic adsorption column experiments, the material exhibited up to 99% removal in simulated wastewater for up to 30days, demonstrating the great adsorption potential of NH-CeAIS-10 in engineering applications.

Comparison of arsenate and arsenite removal behaviours and mechanisms from water by Fe[sbnd]La binary composite (hydr)oxides

The present study compares the performances and mechanisms of As(V) adsorption with As(III) removal by a series of FeLa binary composite (hydr)oxides. The As(V) and As(III) adsorption properties were studied by batch adsorption experiments, and their adsorption mechanisms were explored by SEM-EDS, FTIR, XRD and XPS. The FeLa binary composite (hydr)oxides exhibited excellent As(V) removal performances, and their adsorption properties of As(V) were obviously enhanced with increasing La contents. However, their As(III) removal performances were extremely poor, and the increase of Fe contents could not significantly affect As(III) adsorption performances. The adsorption processes of As(V) were rapid, but the As(III) adsorption were slower. The maximum adsorption capacities of As(V) on Fe/La 3:1, Fe/La 1:1, and Fe/La 1:3 were 166.69, 271.65 and 360.81 mg/g, respectively, and those of As(III) were 30.71, 26.44 and 28.64 mg/g, respectively. Solution pH and presence of PO43−, and citrate can clearly influence the removal efficiencies of As(V) and As(III). The predominant mechanisms of As(V) were the formation of LaAsO4 through ligand exchange reactions under all experimental conditions and coprecipitation of La(III) and As(V) under acidic and neutral conditions, while the formation of inner-sphere surface complexes through ligand exchange reactions between Fe–OH groups and As(III) contributed to the As(III) removal. This work emphasizes the different adsorption properties between As(V) and As(III) by FeLa composite (hydr)oxides, and indicates great application potential in As(V) water treatment and the need for pretreatment for As(III) removal, such as pre-oxidation of As(III) to As(V).

Highly efficient arsenic adsorption onto Mg/Al/Fe layered double hydroxides: Kinetics, isotherm, XPS and Mössbauer spectroscopies

The adsorption of arsenate onto a Mg/Al/Fe layered double hydroxide (Fe-LDH) was studied at different anion concentration, pH, temperature and stirring rate. Different characterization techniques such as FT-IR, X-ray diffraction, XPS and Mössbauer spectroscopies, and zeta potential measurements were used for determining the mechanism of arsenate adsorption onto the studied solid. Two mechanisms are postulated: a) anion exchange reactions with chloride and hydroxyl ions of the interlayer space, and b) ligand exchange reactions with formation of inner-sphere complexes on the Fe-LDH surfaces, with participation of Fe(III) ions from the structure. Arsenate adsorption on Fe-LDH was dependent on the initial pH and the concentration, but was independent of the stirring rate and temperature. Fe-LDH exhibited excellent As(V) removal capacity, much higher than other adsorbents reported in the literature. A dose of 10 g L−1 Fe-LDH was sufficient to reach a percentage removal higher than 95 % for a concentration of arsenic of 1 × 10−4 M found in certain places in Argentina, obtaining residual arsenate values below the recommended World Health Organization limit (0.01 mg L−1). Although the material dissolves at low pH, its high arsenate removal efficiency, the low cost and the green and sustainable characteristics of the material make it an effective adsorbent for the treatment of arsenic contaminated waters.

On the formation of inner-sphere solvation complexes in dilute acetonitrile solutions of the Hg(NO3)2 and Hg(TfO)2 salts: a Molecular Dynamics study

The solvation properties of dilute acetonitrile solutions of the Hg(NO3)2 and Hg(TfO)2 salts have been investigated by using Molecular Dynamics simulations. The Hg2+ ion in acetonitrile was found to coordinate both counterions and acetonitrile molecules in its first solvation sphere by forming inner-sphere complexes. However, different geometries of the Hg2+ solvation polyhedra are formed depending on the counterion: in the Hg(NO3)2 salt solution, Hg2+ forms a 8-fold cluster of acetonitrile and nitrate ligands with a square antiprism symmetry, while in the system containing the Hg(TfO)2 salts, the Hg2+ solvation shell is composed of eight ligands arranged in a C2 symmetry.

Comparative Sb(V) removal efficacy of different iron oxides from textile wastewater: effects of co-existing anions and dye compounds.

Elevated Sb(V) concentration in textile wastewater is a growing environmental concern worldwide and has received wider attention in recent years. Iron oxides possess appealing characteristics as efficient and cost-effective adsorbents in large-scale applications. In the present study, Sb(V) adsorption capacity of α-Fe2O3, γ-Fe2O3, and Fe3O4 was compared under experimental conditions close to the practical textile wastewater treatment. Results demonstrated that α-Fe2O3 performed better under different pH values, reaction times, dye compounds, and co-existing ions as compared to γ-Fe2O3 and Fe3O4, and the adsorption equilibrium was achieved within 8h. Sb(V) adsorption is found to be highly pH dependent, and higher removal was achieved in lower pH, indicating the involvement of electrostatic interactions. The pHpzc value of α-Fe2O3 was 7.15, which favored Sb(V) adsorption in practical wastewater having neutral pH value (pH ~ 7). Pseudo-first- and pseudo-second-order described the data and the simulated values of qe fitted well with the experimental values, indicating that pseudo-second-order model described the adsorption kinetics better with R2 (> 0.95) higher than of pseudo-first-order plots. The Langmuir and Freundlich models both described well the sorption data of all the adsorbents, where the R2 values were > 0.90 with a better fit in the Freundlich model for α-Fe2O3, suggesting that the adsorbent has heterogeneous surface characteristics. Similarly, characterizations revealed that the specific surface area, pore volume, and hydroxyl group content in α-Fe2O3 were higher than others, making it easier for contaminants to bind on to the active sites. Furthermore, the effect of dyes and co-existing anions on Sb(V) adsorption was negligible, except for SO42-, CO32-, and PO43- by the formation of inner-sphere complexes with iron oxides through competitive adsorption with [Sb(OH)6]-. Findings from the present study suggested that α-Fe2O3 effectively reduced Sb(V) in textile wastewater and could be a promising alternative for practical textile wastewater treatment.

3D Composite U(VI) Adsorbents Based on Alginate Hydrogels and Oxidized Biochar Obtained from Luffa cylindrica.

3D naturally derived composites consisting of calcium alginate hydrogels (CA) and oxidized biochar obtained from Luffa cylindrica (ox-LC) were synthesized and further evaluated as adsorbents for the removal of U(VI) from aqueous media. Batch-type experiments were conducted to investigate the effect of various physicochemical parameters on the adsorption performance of materials. The maximum adsorption capacity (qmax) was 1.7 mol kg-1 (404.6 mg·g-1) at pH 3.0 for the CA/ox-LC with a 10% wt. ox-LC content. FTIR spectroscopy indicated the formation of inner-sphere complexes between U(VI) and the surface-active moieties existing on both CA and ox-LC, while thermodynamic data revealed that the adsorption process was endothermic and entropy-driven. The experimental data obtained from the adsorption experiments were well-fitted by the Langmuir and Freundlich models. Overall, the produced composites exhibited enhanced adsorption efficiency against U(VI), demonstrating their potential use as effective adsorbents for the recovery of uranium ions from industrial effluents and seawater.

Molecular-scale insight into selenium isotope fractionation caused by adsorption on Fe (oxyhydr)oxides

Selenium (Se) isotopes have recently emerged as a potential proxy for tracing biogeochemical processes and reconstructing the evolution of global Se cycle in the oceans. However, little is known about Se isotope fractionation mechanism during the sequestration of dissolved Se oxyanions by marine ferromanganese oxides that are mainly composed of Fe and Mn (oxyhydr)oxides. Here we elucidate the molecular mechanism governing equilibrium Se isotope fractionation during adsorption on 2-line ferrihydrite, by combining isotope ratio measurements, extended X-ray absorption fine structure (EXAFS) analyses, and high level quantum chemical calculations. Results show that Se isotopes can be fractionated 0.89‰ (Δ82/76Seaqueous-adsorbed) with enrichment of lighter isotopes in the solid phase during the adsorption of Se(IV) on 2-line ferrihydrite, which is primarily driven by the formation of bidentate-binuclear inner-sphere complexes. By contrast, little or no Se isotope fractionation (<0.2‰) was observed during Se(VI) adsorption due to the outer-sphere complexation. In combination with previous results, our findings would provide molecular-scale insights into Se isotope compositions in marine ferromanganese oxides and lead to an improved understanding of Se biogeochemical cycle in the ocean. Our study also has an implication for the systematical understanding of mechanisms governing isotope fractionations of other metal oxyanions like Mo, which highlights the controls of their proton dissociation constants, electronic configurations, and radius ratios. This would improve our understanding for isotope signatures of metals in the dissolved species and the adsorbed sinks in modern and ancient environments.

The adsorption behavior and mechanism for arsenate by lanthanum-loaded biochar with different modification methods

Lanthanum (La)-loaded biochar (BC) was considered as an efficient adsorbent for phosphate removal in wastewater. Arsenate has a similar chemical structure to phosphate, however, performance and mechanisms of arsenate adsorption onto La-doped biochar are less studied and remain unclear. In this study, La-modified biochar (BC) was prepared using two dinstinct methods: pyrolysis of LaNO3-doped rice husk (pre-pyrolysis modification, referred to as La-BC) and pyrolysis of LaNO3-doped rice husk biochar (post-pyrolysis modification, referred to as BC-La). Isotherm experiments showed that the maximum arsenate adsorption content onto La-BC and BC-La was similar, respectively of 21.3 mg g−1 and 16.5 mg g−1 at pH = 5. Combined results of SEM-EDS, FTIR, and XPS analyzing revealed that La oxides and hydroxides loaded on BC played a vital role in arsenate adsorption. Electrostatic attraction and ligand exchange were considered as key mechanisms for arsenate adsorption. Compared to La-BC, the results revealed that La oxides/hydroxides exhibited more crystalline structures on BC-La. Moreover, the BC-La displayed more efficient adsorption capabilities over a wider pH range (pH 4–10) than La-BC. The XPS O1s spectra analysis confirmed the formation of different inner-sphere complexes on La-BC and BC-La. Results of this study revealed mechanisms of arsenate adsorption onto La-modified biochar, and highlighted that the adsorption behavior of arsenate onto La-modified biochar could be significantly influenced by modification methods.

Unraveling the Np(V) sorption on ZrO2: A batch, spectroscopic and modeling combined approach

The interactions of the long-lived actinide neptunium with the corrosion product zirconia (ZrO2) have to be considered in the safety assessment of a repository for radioactive waste. The sorption of Np(V) on ZrO2 was investigated in the absence of carbonate at the macroscopic and molecular scale. At the macroscopic level, the Np(V) uptake was independent of ionic strength and the isoelectric point of the pristine zirconia was increased, both suggesting the presence of inner-sphere Np(V) surface complexes. The Np(V) sorption isotherms indicated the presence of strong and weak sorption sites. Molecular level information were derived from in situ attenuated total reflection Fourier-transform infrared spectroscopy and extended X-ray absorption fine structure spectroscopy (EXAFS), which confirmed the presence of Np(V) inner-sphere complexes. EXAFS experiments revealed the formation of a bidentate inner-sphere surface complex in the weak sorption site regime. The derived information at the macroscopic and molecular levels were used to parametrize a charge distribution multi-site complexation (CD-MUSIC) model. The derived thermodynamic constants can help to better predict the environmental fate of Np(V) in the context of nuclear waste repository assessments and can also support the appraisal of safety-relevant scenarios for the extended interim storage of spent nuclear fuel.

Highly efficient adsorption of arsenite from aqueous by zirconia modified activated carbon

In the present study, activated carbon decorated with zirconia nanoparticle composite (ZrO2/AC) have been prepared using hydrothermal method and then utilized as an adsorbent for the removal of arsenite from aqueous solution. The composite is composed of highly agglomerated ZrO2 particles on AC surface. The high surface area of the synthesized adsorbent results in its high adsorption capacity toward arsenite. Adsorption isotherm and kinetic data of arsenite adsorption process can be well fitted to the Langmuir isotherm with maximum monolayer adsorption capacity of 64.00 mg.g-1. The experimental results suggest that the adsorption process of arsenite onto ZrO2/AC material involves the formation of both outer-sphere and inner-sphere complexes between arsenite and adsorbent. The high adsorption ability toward arsenite as well as the high recyclable nature of this material makes it a potential alternative material for the removal of toxic heavy metals from wastewater.

The Removal of Phosphate from Aqueous Solutions by Sepiolite/ZrO2 Composites: Adsorption Behavior and Mechanism

The sepiolite/ZrO2 composites were prepared by sepiolite (Sep) modification with zirconium propoxide in toluene at room temperature for 24 h (Sep–ZrI) or 95 °C for 4 h (sample Sep–ZrII). The efficiency of the obtained composites for the removal of phosphate from aqueous solutions at initial pH = 4 and pH = 8 was investigated. Characterization of the samples shows that synthesis at a higher temperature for a shorter time provides a slightly higher content of amorphous Zr phase, which is deposited on the sepiolite fibers as a thin layer and agglomerated nanoparticles. Compared to Sep, the composites have a lower point of zero charge and higher specific surface area and pore volume. The adsorption kinetics follow the pseudo second-order model. The adsorption capacities of the composites are approximately the same at both initial pH and higher at initial pH = 4 than at pH = 8. The XPS and ATR-FTIR of Sep–ZrI before and after adsorption identifies the formation of inner-sphere complexes as the mechanism of phosphate adsorption. The slow release during desorption with NaOH solution confirms the strong bonds of the phosphates with the surface of the composites.

Novel Application of MnO2–H2O2 System for Highly Efficient Arsenic Adsorption and Oxidation

A novel manganese dioxide–hydrogen peroxide (MnO2–H2O2) system was developed for effective Arsenic (As) removal. Under the specified conditions of no external mechanical stirring, a trace H2O2 concentration of 0.015 wt%, and a MnO2 concentration of 25 mg/L, high removal efficiency (88%) of As (100 µg/L) was achieved by the MnO2–H2O2 system within 30 min, which differs from conventional adsorption processes that require external mechanical stirring and conventional arsenite (As (III)) oxidation–adsorption processes that require high quantities of oxidants (such as ozone) and specially synthesized adsorbents/catalysts. The high removal efficiency of As (III) by the MnO2–H2O2 system was attributed to the turbulent conditions precipitated by the extensively generated oxygen (O2) from the catalytic decomposition of H2O2, the efficient adsorption of As on the surface of MnO2, and the effective generation of reactive radicals including hydroxyl and superoxide radicals (•OH and •O2−). Moreover, the MnO2 adsorbents before and after As removal were characterized systematically, and the generated radicals were verified using electron spin resonance (ESR). The results showed that the formation of inner-sphere surface complexes by the surface hydroxyl groups of MnO2 particles and As was responsible for the effective As adsorption process, and the oxidation of As (III) to arsenate (As (V)) was achieved via the generated radicals. The influences of representative environmental factors on As removal performance and the application of the MnO2–H2O2 system in river water and ground water were further studied and tested. In conclusion, the MnO2–H2O2 system offers several advantages, including low cost, ease of operation, and strong environmental adaptability, making it highly promising for practical water treatment applications.

In situ growth of NH2-MIL-101 metal organic frameworks on biochar for glyphosate adsorption

We fabricated a novel adsorbent to remove glyphosate (PMG) in solution by in situ growing of NH2-MIL-101 metal-organic framework on biochar derived by the calcination of waste rice husk (hereafter NMBC61 formulated as NH2-MIL-101: BC = 6:1 ratio). The new adsorbent was systematically characterized by atomic, molecular spectroscopic and conventional experimental methods. The PMG adsorption efficiency on NMBC61 was examined as a function of contact time, solution pH, temperature, matrix solutes, and substrate concentration. The modification of amino group significantly improved the adsorption performance of the material. The PMG adsorption data were modeled using Langmuir isotherm and pseudo-second-order kinetics formulations. The maximum adsorption capacities of NMBC61 at 323 K for PMG is 186.71 mg g−1. The PMG adsorption did not significantly interfere with NO3−, Cl−, HCOO−, and citric acid in the solution matrix; SO42− show an intermediate interfering behavior. However, PMG adsorption interferes significantly in the presence of H2PO42− and citric acid. The contrasting interfering patterns show the nature of surface bonding in PMG adsorption on NBMC61. The subtilties arisen between surface –NH2 and –OH sites on PMG adsorption were resolved by IR and XPS spectral data. The PMG adsorbed on NBMC61 via ligand exchange by inner-sphere surface complex formation. When foreign solutes show similar surface complexing, they interfere with PMG adsorption. Based on the adsorption experiments and density functional theory (DFT) calculations, the van der Waals (vdW) interactions and hydrogen bonding were assumed to be involved in the adsorption. NBMC61 shows over 83% PMG removal efficiency at the end of three cycles. The NMBC61 show optimal PMG adsorption between pH 2 and 6 with minimal interference from the solution matrix. Therefore, NBMC61 has the potential in treating organic pollutants found in natural and wastewaters efficiently with minimal pre-treatment steps.