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

New sulfonated covalent organic framework for highly effective As(III) removal from water

The goal of taking out As(III) from water is to reduce the detriment that poisonous metals can do to people and nature. A substance that can absorb As(III), TFPOTDB-SO3H, was made by combining 2,5-diaminobenzenesulfonic acid and 2,4,6-tris-(4-formylphenoxy)-1,3,5-triazine in a reaction that joins molecules together. This substance can adsorb As(III) very well and has excellent qualities like being easy to use again, separate substances, and filter out liquids. At pH = 8 and at room temperature, TFPOTDB-SO3H adsorbed a lot of As(III). It achieved a removal rate of 97.1 % within 10 min and could adsorb up to 344.8 mg/g. A research was conducted to investigate the effect of co-existing anions on the elimination of arsenic. The findings indicated that the presence of anions had a minimal adverse impact, reducing As(III) uptake by approximately 1-7 %. The kinetics of the uptake process were found to be controlled by the quasi-second order kinetic model, while the Langmuir isotherm model validated that the mechanism for As(III) removal was monolayer chemisorption. According to the thermodynamic analysis, the adsorption process was endothermic and occurred spontaneously. Moreover, even after 4 successive adsorption-desorption cycles, the adsorbent preserved a substantial uptake productivity of 88.86 % for As(III). The results collectively indicate that TFPOTDB-SO3H holds considerable promise for the efficient adsorption and elimination of As(III) ions from wastewater.

Q-switched pulse operation in erbium-doped fiber laser subject to zirconia (ZrO2) nanoparticles-based saturable absorber

In this paper, the zirconia (ZrO2) nanoparticles-based saturable-absorber (SA) have been incorporated in an erbium-doped fiber laser (EDFL) cavity for achieving a Q-switched pulse operation. The implementation of the zirconia nanoparticles-based powder on the fiber facet was accomplished using the index-matching gel's adhesion effect. The incorporation of SA in the laser cavity yielded a stable and self-starting Q-switched operation under 19.36 mW pump power that corresponded to the emission wavelength of 1557.29 nm. Additionally, it was observed that the EDFL's emission wavelength tuned from 1557.29 nm to 1562.3 nm , and the repetition rates and pulse width ranged from 61.2 to 130 kHz and 7.9 to 3.6 μs, respectively, as the pump power was increased from 19.36 to 380.16 mW. Measured experimental results reveal that at a maximum pump power of 380.16 mW, the maximum average output power, peak power, and pulse energy were noticed to be 1.17 mW, 2.5 mW, and 9 nJ, respectively. A 52 dB suppression in side bands was found at a pump power of 380.16 mW. Moreover, the stability and threshold tolerance of the EDFL has also been discussed in detail. These findings suggest that nanoparticle-based saturable absorbers have potential applications in a pulsed source, making it easier to implement in fiber cavity-based systems.

Simultaneous removal of arsenate and arsenite in water using a novel functional halloysite nanotube composite

This work aims at exploring a novel environment-friendly nanomaterial based on natural clay minerals for arsenic removal in aqueous samples. Halloysite nanotubes (HNTs) were selected as the substrate with Mn oxides loaded on the surface to enhance its arsenic adsorption ability and then grafted onto the SiO₂-coated Fe₃O₄ microsphere to get a just enough magnetic performance facilitating the material's post-treatment. The prepared composite (Fe₃O₄@SiO₂@Mn-HNTs) was extensively characterized by various instruments including Fourier transform infrared spectroscope (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), thermogravimetric analysis (TG), vibrating sample magnetometer (VSM), X-ray photoelectron spectroscope (XPS), and X-ray diffraction (XRD). Batch experiments were carried out to get the optimum test conditions for arsenic adsorption by the composite, including pH, loading amount of Mn oxides, adsorbent dosage, and the co-existing ions. The adsorption of As^III and As^V on Fe₃O₄@SiO₂@Mn-HNTs were both well fitted with the pseudo-second-order kinetic model as well as the Langmuir adsorption isotherm model revealing the chemisorption between arsenic and Fe₃O₄@SiO₂@Mn-HNTs. The adsorption process of As^III and As^V were both endothermic and spontaneous displayed by the thermodynamic study. The capacities of the prepared composite are 3.28 mg g^-1 for As^III and 3.52 mg g^-1 for As^V, respectively, which are comparable or better than those of many reported materials in the references. Toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) tests were carried out to access the secondary environmental risk of the composite and showed that it was quite environmentally stable and can be safely disposed. The composite was successfully applied in environmental water samples indicating its great potential applicability in future.

Zirconia-based nanomaterials: recent developments in synthesis and applications

In the last decade, the whole scientific community has witnessed great advances and progress in the various fields of nanoscience. Among the different nanomaterials, zirconia nanomaterials have found numerous applications as nanocatalysts, nanosensors, adsorbents, etc. Additionally, their exceptional biomedical applications in dentistry and drug delivery, and interesting biological properties, viz. anti-microbial, antioxidant, and anti-cancer activity, have further motivated the researchers to explore their physico-chemical properties using different synthetic pathways. With such an interest in zirconia-based nanomaterials, the present review focuses systematically on different synthesis approaches and their impact on the structure, size, shape, and morphology of these nanomaterials. Broadly, there are two approaches, viz., chemical synthesis which includes hydrothermal, solvothermal, sol-gel, microwave, solution combustion, and co-precipitation methods, and a greener approach which employs bacteria, fungus, and plant parts for the preparation of zirconia nanoparticles. In this review article, the aforementioned methods have been critically analyzed for obtaining specific phases and shapes. The review also incorporates a detailed survey of the applications of zirconia-based nanomaterials. Furthermore, the influence of specific phases, morphology, and the comparison with their counterpart composites for different applications have also been included. Finally, the concluding remarks, prospects and possible scope are given in the last section.

Mesoporous carbon structure impregnated with 2D engineered zirconium: A sustainable adsorbent for the removal of dyes from the aqueous solution

The key designing of new breeds of the adsorbents aimed to improve the physical, chemical and textural morphology along with surface functionalization, selectivity toward the contaminants, and regenerations efficiency. In this aspect, two adsorbents named wet oxidative and ultrasonicated zirconium impregnated composite, have been synthesized through two routes, i.e., wet oxidation and ultrasonication. In wet oxidation method, carbon-based materials are oxidized using an oxidant followed by impregnation, while in ultrasonication assisted route, the impregnation is carried out using acoustic phenomenon. The characterization study revealed that the wet oxidation process is more competent in impregnating zirconium and developing diverse porosity and functionalities. The maximum adsorption capacity of wet oxidative adsorbent was 812 mg/g for Reactive Blue 19 and 203.18 mg/g for Methylene Blue, that accentuated the efficiency of the adsorbent over raw activated carbon. The electrostatic interaction, hydrogen-bonding and ligand exchange phenomenon are the involved adsorption mechanism for dyes. The regeneration study finally asserts that the wet oxidative adsorbent shows an insignificant decrease in its capacity up to the 5^th-cycle (i.e., 87.67% removal at 5^th cycle) as compared to raw AC (46.71% removal at 5th cycle). Further, a continuous fixed-bed column study revealed a significant correlation between experimental breakthrough data and kinetic data. Thus, the developed adsorbent has a sedulous adsorption capacity to remove the most stubborn toxic dyes and can be used in industrial-scale applications.

Enhancing the remarkable adsorption of Pb2+ in a series of sulfonic-functionalized Zr-based MOFs: a combined theoretical and experimental study for elucidating the adsorption mechanism

A series of Zr-based metal-organic frameworks was prepared via the solvothermal route using sulfonic-rich linkers for the efficient capture of Pb²⁺ ions from aqueous medium. The factors affecting adsorption such as the solution pH, adsorbent dosage, contact time, adsorption isotherms, and mechanism were studied. Consequently, the maximum adsorption capacity of Pb²⁺ on the acidified VNU-23 was determined to be 617.3 mg g^-1, which is much higher than that of previously reported adsorbents and MOF materials. Furthermore, the adsorption isotherms and kinetics of the Pb²⁺ ion are in good accordance with the Langmuir and pseudo-second-order kinetic model, suggesting that the uptake of Pb²⁺ is a chemisorption process. The reusability experiments demonstrated the facile recovery of the H⁺⊂VNU-23 material through immersion in an HNO₃ solution (pH = 3), where its Pb²⁺ adsorption efficiency still remained at about 90% of the initial uptake over seven cycles. Remarkably, the adsorption mechanism was elucidated through a combined theoretical and experimental investigation. Accordingly, the Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy connected to energy-dispersive X-ray mapping (SEM-EDX-mapping), and X-ray photoelectron spectroscopy (XPS) analysis of the Pb⊂VNU-23 sample and comparison with H⁺⊂VNU-23 confirmed that the electrostatic interaction occurs via the interaction between the SO₃^- moieties in the framework and the Pb²⁺ ion, leading to the formation of a Pb-O bond. In addition, the density functional theory (DFT) calculations showed the effective affinity of the MOF adsorbent toward the Pb²⁺ ion via the strong driving force mentioned in the experimental studies. Thus, these findings illustrate that H⁺⊂VNU-23 can be employed as a potential adsorbent to eliminate Pb²⁺ ions from wastewater.

Efficient Sorption of Arsenic on Nanostructured Fe-Cu Binary Oxides: Influence of Structure and Crystallinity

To study the structure-performance relationship, a series of nanostructured Fe-Cu binary oxides (FCBOs) were prepared by varying synthesis conditions. The obtained binary oxides were well characterized using X-ray diffraction (XRD), transmission electron microscope (TEM), Brunner-Emmet-Teller (BET), magnetic and Zeta potential measurement techniques. Both As(V) and As(III) sorption on the FCBOs were evaluated by batch tests. Results show that the surface structure and crystallinity of FCBOs are greatly dependent on preparation conditions. The crystallinity of FCBOs gradually increases as the synthesis pH value increasing from 9.0 to 13.0, from amorphous phase to well-crystalline one. Simultaneously, the morphology change of FCBOs from irregular agglomerate to relatively uniform polyhedron has been observed. The sorption of arsenic is greatly influenced by the crystallinity and structure of FCBOs, decreasing with increasing degree of crystallinity. The amorphous FCBO has higher surface hydroxyl density than well-crystalline one, which might be the reason of higher sorption performance. As(V) is sorbed by the FCBOs via formation of inner-sphere surface complexes and As(III) is sorbed through formation of both inner- and outer-sphere surface complexes. This investigation provides new insights into structure-performance relationship of the FCBO system, which are beneficial to develop new and efficient sorbents.

Synthesis of Fe3O4@mZrO2-Re (Re = Y/La/Ce) by Using Uniform Design, Surface Response Methodology, and Orthogonal Design & Its Application for As3+ and As5+ Removal

In this study, iron oxide (Fe₃O₄) was coated with ZrO₂, and doped with three rare earth elements((Y/La/Ce), and a multi-staged rare earth doped zirconia adsorbent was prepared by using uniform design U₁₄, Response Surface methodology, and orthogonal design, to remove As³⁺ and As⁵⁺ from the aqueous solution. Based on the results of TEM, EDS, XRD, FTIR, and N₂-adsorption desorption test, the best molar ratio of Fe₃O₄:TMAOH:Zirconium butoxide:Y:La:Ce was selected as 1:12:11:1:0.02:0.08. The specific surface area and porosity was 263 m²/g, and 0.156 cm³/g, respectively. The isothermal curves and fitting equation parameters show that Langmuir model, and Redlich Peterson model fitted well. As per calculations of the Langmuir model, the highest adsorption capacities for As³⁺ and As⁵⁺ ions were recorded as 68.33 mg/g, 84.23 mg/g, respectively. The fitting curves and equations of the kinetic models favors the quasi second order kinetic model. Material regeneration was very effective, and even in the last cycle the regeneration capacities of both As³⁺ and As⁵⁺ were 75.15%, and 77.59%, respectively. Adsorption and regeneration results suggest that adsorbent has easy synthesis method, and reusable, so it can be used as a potential adsorbent for the removal of arsenic from aqueous solution.

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.

Scale-up one-pot synthesis of waste collagen and apple pomace pectin incorporated pentapolymer biocomposites: Roles of waste collagen for elevations of properties and unary/ ternary removals of Ti(IV), As(V), and V(V)

Herein, hazardous solid particulate waste collagenic fibers (SWCFs) of leather industries were incorporated into apple pomace pectin (APPN)-grafted-pentapolymer, i.e., APPN-g-[sodium 2-methylidenebutanedioate(SMBD)-co-N-((3-(isopropylamino)-3-oxopropoxy) methyl) butyramide (CM1)-co-N-(hydroxymethyl)prop-2-enamide (NHMPE)-co-N-(hydroxymethyl)-4-(N-isopropylbutyramido)butanamide (CM2)-co-N-(propan-2-yl)prop-2-enamide NPYPE)/ PENP1], i.e., APPN-g-PENP1/ PENP2, prepared via one-pot facile polymerization of APPN and synthetic monomers, i.e., SMBD, NHMPE, and NPYPE, in aqueous medium, to fabricate an optimum multifunctional hybrid biocomposite adsorbent/ HCOM3. In PENP1, PENP2, and HCOM3, fourth/ CM1 and fifth/ CM2 multifunctional comonomers were anchored in situ. The structures of PENP1, PENP2, HCOM3, CM1, CM2, and metal-ion adsorbed HCOM3; APPN-grafting; SWCF incorporation; and surface properties were analyzed through NMR, XPS, FTIR, XRD, and SEM. The elevated adsorption efficiencies (AEs), reusability, thermostability, swelling, network durability, and crosslink density of HCOM3 were attributed to variable functionalities of SWCF/ APPN, explored by DLS and TGA, swelling, network, and thermodynamic parameters. Compared to SWCF, APPN, PENP1, and PENP2, the elevated AEs and reusability compelled HCOM3 as more suitable for scalable waste management. The maximum AEs, i.e., 171.79, 180.47, and 177.27 mg g^-1, for Ti(IV), As(V), and V(V) at pH_op = 7.0, 3.0, and 5.0, respectively, within 5-100 mg L^-1 and at 298 K for 25 mg HCOM3 deteriorated during ternary adsorption by the antagonistic effects.

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.

Radioactive cesium ion removal from wastewater using polymer metal oxide composites

Radioactive cesium ion (Cs-137) removal from wastewater was investigated by novel composite adsorbents, chitosan-bone powder (CS-KT) and chitosan-bone powder-iron oxide (CS-KT-M) at 25 and 50 °C. The characterization of adsorbents was performed by Fourier-Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Brunauer-Emmett-Teller and Barrett-Joyner-Hallenda (BET-BJH), and Atomic Force Microscopy (AFM) analyses. While BET surface areas of CS-KT and CS-KT-M adsorbents were found to be 131.5 and 144.9 m²/g, respectively, average pore size and pore volume values were 4.69 nm/0.154 cm³/g and 7.49 nm/0.271 cm³/g, respectively. Amongst Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) models, Langmuir model fits well for Cs⁺ ion sorption by these adsorbents. The maximum adsorption capacity obtained from Langmuir adsorption isotherm was 0.98 × 10^-4 mol/g at 25 °C, and 1.16 × 10^-4 mol/g at 50 °C for CS-KT; it was found to be 1.79 × 10^-4 mol/g at 25 °C and 2.24 × 10^-4 mol/g at 50 °C for CS-KT-M. FT-IR analyses showed that Cs⁺ sorption occurs by its interaction with CO₃^2-, PO₄^3- and -NH₂ groups. The average adsorption energy "E" was calculated as ca.11 kJ/mol from D-R adsorption isotherm. The adsorption kinetics was interpreted well by pseudo-second order model.

Adsorption of arsenic from aqueous solution using a zero-valent iron material modified by the ionic liquid [Hmim]SbF6

The environmental and health impacts caused by arsenic (As) in wastewater make it necessary to carefully manage As wastes. In the present work, a composite of the ionic liquid [Hmim]SbF₆ and nano-iron (H/Fe) was used as an adsorbent to remove As(v) from aqueous solution. To better understand the removal effect of H/Fe on As(v) in aqueous solution, the reaction parameters of pH, reaction temperature, time and H/Fe dosage were systematically analyzed in detail. The results show that H/Fe has significant removal efficiency toward As(v), and that the adsorption of As(v) by 0.5 g H/Fe reaches its maximum adsorption capacity within 2 h. The adsorption of As(v) on H/Fe is a non-linear, time-varying process. The initial adsorption reaction is fast; however, unlike at the beginning, the later reaction involves sustained slow absorption, resulting in a distinct two-phase adsorption characteristic. Redox reaction may be one of the mechanisms responsible for the slow adsorption of As(v) on H/Fe. At the same time, the As(v) removal effect of H/Fe is greatly restricted by the pH. Electrostatic adsorption, adsorption co-precipitation and redox reactions act together on H/Fe in the As(v) removal process. This study provides a basis for further clarifying the adsorption, adsorption rules and mechanism of As(v) on H/Fe and a feasible method for the improvement of As(v) removal efficiency of zero-valent iron materials.

N-Alkylated chitosan coupled to the liquid-phase polymer-based retention (LPR) technique to remove arsenic (V) from aqueous systems

Water-soluble polymer based on alkylated chitosan with a quaternary ammonium group (Ch-QAG) was prepared, characterized, and applied to remove arsenate ions from aqueous solution by LPR technique. The arsenic removal was performed by the washing method (WM) and enrichment method (EM). Through the WM, studies of the pH and variation in the concentrations of interferents and arsenate ions were carried out. The effect of the removal of arsenate ions in simulated water was determined from the Camarones River in northern Chile. Ch-QAG showed high affinity for binding arsenate species (99% of removal) at pH 11.0 at a molar ratio of 20:1 polymer: As(V). High selectivity was also observed in the presence of interfering ions such as Cl^-, SO₄^2-, and PO₄^3-, resulting in a removal rate over 80% at percentages over 95% for a concentration of 100 mg L^-1 of As (V). The maximum retention capacity obtained was 112, 105, and 98 mg g^-1 for three load cycles. The retention percentage for simulated water was 46.3% at a concentration of 1300 μ g L^-1. In conclusion, the results presented in this study show that using Ch-QAG with ultrafiltration membranes is a great alternative to remove As (V) at high removal rates.

Simultaneous removal of Congo red and cadmium(II) from aqueous solutions using graphene oxide-silica composite as a multifunctional adsorbent

Graphene oxide is a very high capacity adsorbent due to its functional groups and π-π interactions with other compounds. Adsorption capacity of graphene oxide, however, can be further enhanced by having synergistic effects through the use of mixed-matrix composite. In this study, silica-decorated graphene oxide (SGO) was used as a high-efficiency adsorbent to remove Congo red (CR) and Cadmium (II) from aqueous solutions. The effects of solution initial concentration (20 to 120 mg/l), solution pH (pH 2 to 7), adsorption duration (0 to 140 min) and temperature (298 to 323 K) were measured in order to optimize the adsorption conditions using the SGO adsorbent. Morphological analysis indicated that the silica nanoparticles could be dispersed uniformly on the graphene oxide surfaces. The maximum capacities of adsorbent for effective removal of Cd (II) and CR were 43.45 and 333.33 mg/g based on Freundlich and Langmuir isotherms, respectively. Langmuir and Freundlich isotherms displayed the highest values of Q_max for CR and Cd (II) adsorption in this study, which indicated monolayer adsorption of CR and multilayer adsorption of Cd (II) onto the SGO, respectively. Thermodynamic study showed that the enthalpy (ΔH) and Gibbs free energy(ΔG) values of the adsorption process for both pollutants were negative, suggesting that the process was spontaneous and exothermic in nature. This study showed active sites of SGO (π-π, hydroxyl, carboxyl, ketone, silane-based functional groups) contributed to an enormous enhancement in simultaneous removal of CR and Cd (II) from an aqueous solution, Therefore, SGO can be considered as a promising adsorbent for future water pollution control and removal of hazardous materials from aqueous solutions.

Preparation of a Novel Zn(II)-Imidazole Framework as an Efficient and Regenerative Adsorbent for Pb, Hg, and As Ion Removal From Water

An outstanding metal-organic framework sorbent (Zn-MOF) was prepared using Zn²⁺ and 3-amino-5-mercapto-1,2,4-triazole to eliminate toxic metal ions from water. Zn-MOF was detected via using Fourier-transform infrared (FTIR) spectroscopy, field-emission scanning electron microscopy (FESEM), Brunauer-Emmett-Teller (BET) analysis, and X-ray photoelectron spectroscopy (XPS). Zn-MOF is stable and has a very large surface area. The uptake properties of Zn-MOF were investigated. The maximum uptake capacity of Zn-MOF for Pb, Hg, and As ions was 1097, 32, and 718 mg/g, respectively. This was obtained at pH = 4, 5, and 6, respectively. The adsorption data is in good agreement with the Langmuir and pseudo-second-order rate models, indicating that the uptake process of Zn-MOF for toxic metal ions was a single layer uptake on a uniform surface via exchange of valence electrons. Thermodynamics shows that the uptake process is autogenic and endothermic. Zn-MOF can be reused at least 6 times. Mercury and lead strongly coordinated with Zn-MOF. The interaction between arsenic and Zn-MOF is weak chemical coordination and ion exchange. Zn-MOF has wide application prospects for toxic metal ion elimination.

Zirconia-Assisted Pyrolysis of Coffee Waste in CO2 Environment for the Simultaneous Production of Fuel Gas and Composite Adsorbent

This work newly employed monoclinic zirconia (ZrO₂) as a promoter to improve CO₂ pyrolysis of coffee waste (CW). The CO₂ pyrolysis of CW presented the high level of CO production (14.3 mol%) during two stages of non-isothermal (280 to 700 °C) and isothermal pyrolysis (kept at 700 °C). At the same condition, the incorporation of ZrO₂ improved the CO generation up to about twice that of CW (29.5 mol%) by possibly inducing more conversion of pyrolytic oil into gas. The characterization results exhibited that ZrO₂-impregnated biochar (ZrB) possessed the distinctive surface morphology that highly graphitic- and porous carbon layers were covered by ZrO₂ nanoparticle clusters. In a series of adsorption experiments, ZrB composite showed pH-dependent As(V) adsorption and pH neutralization ability. The adsorption proceeded relatively rapid with 95% removal during 120 min in the early stage, followed by 5% removal in the remaining 240 min. The maximum adsorption capacity was found to be 25.2 mg g^-1 at final pH 8. The reusability and stability of ZrB were demonstrated in the 6 consecutive cycles of adsorption/desorption. As a result, ZrO₂-assisted CO₂ pyrolysis can potentially produce fuel gas with high CO fraction and composite adsorbent suitable for As(V) removal in acidic wastewater.

Rational design, synthesis, adsorption principles and applications of metal oxide adsorbents: a review

The shortage of water resources and increasingly serious water pollution have driven the development of high-efficiency water treatment technology. Among a variety of technologies, adsorption is widely used in environmental remediation. As a class of typical adsorbents, metal oxides have been developed for a long time and continued to attract widespread attention, since they have unique physicochemical properties, including abundant surface active sites, high chemical stability, and adjustable shape and size. In this review, the basic principles of the adsorption process will be first elucidated, including affecting factors, evaluation index, adsorption mechanisms, and common kinetic and isotherm models. Then, the adsorption properties of several typical metal oxides, and key parameters affecting the adsorption performance such as particle/pore size, morphology, functionalization and modification, supports and calcination temperature will be discussed, as well as their application in the removal of various inorganic and organic contaminants. In addition, desorption and recycling of the spent adsorbent are summarized. Finally, the future development of metal oxide based adsorbents is also discussed.

Synthesis of mesoporous MFI zeolite via bacterial cellulose-derived carbon templating for fast adsorption of formaldehyde

Mesoporous ZSM-5 (MFI) zeolite was synthesized by using bacterial cellulose-derived activated carbon (BC-AC500) with a high surface area as a hard template. Different ratios of BC-AC500 and zeolite precursor gel were prepared in a Teflon-lined autoclave and crystallized at 180 °C for 48 h in a rotating oven. The physicochemical properties of the samples were characterized by x-ray diffraction (XRD), scanning/transmission electron microscopies (SEM/TEM), and N₂ physisorption techniques. It was found that the mesoporous ZSM-5 zeolites have a specific surface area of 184-190 m²/g, a high mesopore volume of 0.120-0.956 ml/g and a wide pore size distribution ranging from 5 to 100 nm with a maximum at approximately 25.3 nm. The successfully made mesoporous ZSM-5 was tested as an adsorbent for formaldehyde adsorption in batch mode. The mesoporous ZSM-5 zeolite made from bacterial cellulose-derived activated carbon showed significantly faster adsorption kinetics than conventional ZSM-5 (0.0081 vs. 0.0007 g/mg min, respectively). The prepared material has an adsorption capacity of 98 mg/g and is highly reusable. The reported mesoporous ZSM-5 zeolites can be deployed for the rapid removal of toxic organics from wastewater when urgently needed, e.g., under breakthrough conditions.

Arsenate removal from aqueous solutions by cuttlebone/copper oxide nanobiocomposite

This study aims to illustrate the preparation of a new nanobiocomposite by incorporating copper oxide nanoparticles into cuttlebone matrix (CB/CuO NPs), and it was tested to define how effective it was to adsorb and remove arsenate from aqueous systems. CB is the bone tissue of cuttlefish with high porosity, permeability, and low cost. CuO NPs have been introduced as an effective arsenate adsorbent. Producing nanocomposite by introducing of CuO NPs in the structure of CB enhanced their stability and facilitated their separation from solution. Incorporation of CuO NPs in the structure of CB enhanced the adsorption capacity of CB. The adsorption data were fitted with both Langmuir and Freundlich isotherms, but Langmuir isotherm exhibited better matching rather than Freundlich isotherm. The maximum adsorption capacity (q_max) was calculated from Langmuir adsorption isotherm which was around 25.13 mg g^-1. Kinetic data fitted well to the pseudo-second-order reaction model. The results indicate that the possible mechanism of arsenate adsorption on CB/CuO is through development of inner sphere complex. Simple preparation and abundant and good adsorption capacity in the presence of calcium ions indicate that the CB/CuO is suitable for removal of arsenate from contaminated drinking water.

Construction of electrochemical sensing interface towards Cd(II) based on activated g-C3N4 nanosheets: considering the effects of exfoliation and protonation treatment

There is an urgent need to construct highly selective low-cost sensors for fast detection of toxic metal ions such as cadmium. When compared with 3D bulk materials, 2D layered materials after activation treatments show superior performances for electrochemical metal ion detection. The bulk graphitic carbon nitride (hereafter b-g-C₃N₄) was prepared by thermal polymerization with urea as a precursor; it was then activated through ultrasonic liquid exfoliation and protonation which resulted in successful fabrication of activated ultrathin g-C₃N₄ nanosheets (hereafter a-g-C₃N₄). The a-g-C₃N₄-modified glassy carbon electrode demonstrates excellent electrochemical performances for Cd²⁺ detection with 22.668 μA/μM sensitivity and 3.9 nM LOD (S/N = 3) due to high specific surface area and active sites created on the 2D layered structure. The chemical interference of Pb²⁺, Cu²⁺, and Hg²⁺ on Cd²⁺ detection was minimal. We have also measured Cd²⁺ in natural water and rice samples using the newly developed a-g-C₃N₄-modified electrode with high spike recoveries. Our results demonstrate the potential applications of newly developed a-g-C₃N₄-modified electrode for rapid detection of toxic metal ions in different sample matrixes. Graphical Abstract The activated g-C₃N₄ nanosheets (a-g-C₃N₄) were synthesized and used to construct electrochemical sensors with high sensitivity and anti-interference performance.