Materials For Water Purification Research Articles

Carbothermally synthesized, lignin biochar-based, embedded and surface deposited nano zero-valent iron composites: Comparative material characterization, selective gas adsorption and nitroaromatics remediation

Biochar (BC) with nanoscale zero valent iron (nZVI) incorporation offers advantageous materials for water purification. Even though the most common approach for nZVI incorporation is the deposition on the carrier surface, embedding in the support matrix has also been reported. However, the behavior of the embedded material in contaminant removal has not been adequately studied while characteristics and the remediation capabilities of the two materials have not been compared. Present study focuses on preparing and extensively characterizing two materials: nZVI embedded in (Lig-e-nZVI) and surface deposited on (Lig-s-nZVI) lignin BC with subsequent comparative study of remedial action for two nitroaromatics, p-nitroaniline (pNA) and p-nitrophenol (pNP). The synthesis of Lig-e-nZVI and Lig-s-nZVI involved simultaneous and subsequent pyrolysis of lignin and carbothermal reduction of the iron salt, respectively. Lig-e-nZVI showed enhanced porosity. XRD confirmed the formation of Fe0. HR-TEM images proved the core-shell structure of nZVI, and an interlayer spacing of 0.36nm of the shell verified that the Fe0 particles are encapsulated with graphene while an iron carbide inner layer was also observed, thinner in Lig-e-nZVI and thicker in Lig-s-nZVI. Band gap energy of 2.54eV suggested a photocatalytic activity of both materials. Best fitted Sips isotherms showed 23.1 and 13.1mgg-1 capacities for Lig-s-nZVI in pNP and pNA adsorption respectively. Highest stability was portrayed by Lig-e-nZVI over 4 regeneration cycles. The physicochemical features of the developed materials further enable selective gas adsorption. Findings provide new insights into physicochemical characteristics and remedial actions of differently synthesized nZVI-BC composites.

Solar-Driven Evaporator With "Starburst Turbine" Design Featuring Directional Salt Crystallization, Antibacterial, and Catalytic Multifunctionality for Efficient Water Purification.

Facing the global challenge of water scarcity, solar-driven desalination is considered a sustainable technology for obtaining freshwater from seawater. However, issues such as uncontrolled salt crystallization and bacterial contamination limit its efficiency and practicality. This study proposes an innovative solar-driven evaporator designed to address these challenges using optimized shape design and advanced photothermal materials. Based on finite element analyses, cylindrical evaporators with a "Starburst Turbine" shape are designed and fabricated, achieving directional salt crystallization and a record-breaking water collection rate of 3.56kg m-2 h-1 and an evaporation rate of 4.57kg m-2 h-1 under one sun illumination. During continuous 60-h illumination tests, the evaporator maintained a stable evaporation rate, attributed to its excellent directional salt crystallization capability. Additionally, the evaporator demonstrates superior photodynamic antibacterial performance and photocatalytic degradation of organic pollutants. Under one sun illumination for 1 h, it achieves 100% sterilization of S. aureus and E. coli, and a 95.4% degradation of methylene blue (MB), demonstrating its potential to purify various wastewater types. These findings underscore the significant scientific and practical value of integrating antibacterial and photocatalytic functions into solar water purification materials, providing a sustainable solution to global water scarcity challenges and environmental protection.

Interface engineering of laminated redox-copolymers for electrochemical remediation of perfluoroalkyl substances

Redox polymers now show promise for selective removal of perfluoroalkyl substances from a complex aqueous matrix at high energy efficiency and no secondary pollution. However, self-agglomeration of redox polymers is a dominating barrier to constructing a low-cost, stable system in practical applications. Herein, we introduce polymer interface engineering strategy to enhance the activity of amine functionalities and nitrous oxide radicals in copolymers composed of 4-methacryloyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl and 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine. The grafted laminated redox polymer on multi-walled carbon nanotubes (termed MWCNT-g-P(TMPMA-co-TMA)) via free-radical polymerization demonstrated a 19.1–59.9 % increase in the electrosorption capacity with a maximum value (Qm) of 725.09 mg g−1 and a pseudo-first-order rate constant k1 = 1.46 min−1 and sustainable regeneration efficiency at ∼80 %. The core–shell structure of MWCNT-g-P(TMPMA-co-TMA) with a laminated redox polymer layer of ∼5 nm processed a low charge transfer resistance, which is expected to contribute to the enhanced capture performance and stability. An integrated system consisting of a MWCNT-g-P(TMPMA-co-TMA) electrode and a boron-doped diamond electrode can efficiently separate and degrade trace-concentration PFOA from industrial wastewater at high mineralization efficiency. This work provides insight into the design and optimization of redox active materials for water purification and beyond.

Full-spectrum plasmonic semiconductor with stabilized oxygen vacancies enables VOCs purification for durable clean water capture

To mitigate health risks associated with volatile organic compounds (VOCs) in solar-driven water evaporation, we developed Au/WO2.72 material with full-spectrum absorption capabilities and dual photothermal and photocatalytic properties. Injecting hot electrons from Au nanoparticles (NPs) into WO2.72 preserves oxygen vacancies, thus maintaining the plasmonic effect and significantly reducing hot electron relaxation. This leads to enhanced purification of VOCs. The MF-Au/WO2.72 water evaporator, constructed on a melamine–formaldehyde (MF) substrate, demonstrated a water evaporation rate of 1.36 kg m-2 h−1 and stability over 6 h daily for 12 days under one sun irradiation. Importantly, it achieved a 92.9 % removal efficiency for phenol VOCs. Outdoor experiments validated its effectiveness in organic wastewater purification and seawater desalination, highlighting its potential for efficient and clean water production by simultaneously removing VOCs during the evaporation process. This work provides valuable insights into utilizing plasmonic-coupling materials for solar water purification.

Green carbon-based adsorbents for water treatment in Sub-Saharan Africa

Abstract As underlined by the United Nations Sustainable Development Goals (UN SDGs), providing safe and clean potable water remains a significant concern in developing regions of the world, especially Sub-Saharan Africa. Extensive research has been done on this subject in Africa. The concept of sustainable chemistry towards solving another pressing issue in Africa – waste management – led to the decision to investigate green carbon-based materials for water purification on the continent. The conversion of “waste to wealth” is a practical means of achieving proper waste management at a reasonable cost. Low-cost adsorbents such as biochar, activated carbons, graphene and carbon composites, with high surface area, porosity and efficiency have been generated from agricultural waste and biomass, carbon-rich geological materials, carbonaceous polymeric materials, and hydrocarbons/petroleum by-products, using simple thermal and/or green chemical reaction protocols. Several drawbacks have hindered the development and utilization of adsorbents for the treatment of polluted water, including chemical fouling, loss of activity, poor reusability, difficulty associated with sorbent regeneration, production of secondary pollutants, toxicities caused by exposure to sorbent residues, and inability to deal with heavily polluted water. However, the use of adsorbents is still widely acclaimed as an efficient and cleaner method among other existing water treatment options such as extraction, chemical oxidation, bioremediation, and photocatalytic degradation. This paper outlines the research carried out by Sub-Saharan African scientists to proffer solutions to water pollution using green carbon-based adsorbents and discusses the breakthroughs, challenges, and future prospects.

Preparation of grape branch-derived porous carbon by one-step blending and its multifunctional applications

In this study, an innovative methodology is presented for the rapid one-step synthesis of carbon materials with high specific surface area through doping and activation processes, utilizing ball milling techniques to reduce the particle size of the materials effectively and to achieve activation and doping. Nitrogen-doped grape branch carbon (NGBC) was characterized by abundant micro- and mesoporous structures with specific surface areas up to 1364 m2/g and high nitrogen content (atomic fraction of 4.89 %). At pH 8 and room temperature, NGBC showed excellent adsorption performance for malachite green (MG, a cationic dye) and reactive blue 19 (an anionic dye) with adsorption capacities of 409.91 mg/g and 213.36 mg/g, respectively, and the material can be reused several times. The analysis of adsorption kinetics revealed that multiple factors controlled the adsorption process of NGBC on MG, and the analysis of adsorption isotherms showed that the adsorption process was mainly monomolecular layer adsorption. Compared with the common carbon-based adsorbents for biomass currently available on the market, NGBC showed better adsorption efficacy, indicating its great potential for practical application. Further, when NGBC was applied to electrochemical performance tests as supercapacitor electrodes, the introduction of nitrogen significantly improved the specific capacitance and ion transport properties of the porous carbon material, effectively reducing the electrical resistance. At a current density of 0.5 A/g, the nitrogen-doped porous carbon showed a specific capacitance of 258.4 F/g, much higher than that of the undoped 136.8 F/g, as well as a high specific capacitance retention of 90.43 % after 5000 cycles. The sensitivity analysis points out that nitrogen source and labor expenditure are the key factors in the cost components. This research not only provides a simple method for industrialized recovery and reuse of grape branches, but also lays an experimental and theoretical foundation for promoting further applications of biomass waste in the fields of water purification and supercapacitor electrode materials.

Adsorption Behaviour of Pb and Cd on Graphene Oxide Nanoparticle from First-Principle Investigations.

Graphene oxide (GO) is considered as a promising adsorbent material for the removal of metal from aqueous environments. Here, we have used the density functional theory (DFT) approach and a combination of parameters to characterise the interactions of GO with lead (Pb) and cadmium (Cd), i.e., typical harmful metals often found in water. Our model systems consist of a singly and doubly adsorbed neutral (Pb0, Cd0) and charged (Pb2+, Cd2+) atoms adsorbed on the GO nanoparticle of the chemical formula C30H14O15. We show that a single charged metal ion binds more strongly than a neutral atom of the same type. Moreover, to determine the possibility of multiple adsorptions of the GO nanoparticle, two metal atoms of the same species were co-adsorbed on its surface. We found a site-dependent adsorption energy such that when two atoms of the same specie are adsorbed at sites Si and Sj, the binding energy per atom depends on whether one of the two atoms is adsorbed firstly on the Si or Sj sites. Furthermore, the binding energy per atom for the two co-adsorbed atoms of the same specie (i.e., neutral or charged) is less than the binding energy of a singly adsorbed atom. This suggests that atoms may become less likely to be adsorbed on the GO nanoparticle when their concentration increases. We adduce the origin of this observation to be interplay between the metal-metal interaction on the one hand and GO-metal on the other, with the former resulting in less binding for the charged adsorbed metals in particular, due to repulsive interaction between two positively charged ions. The frontier molecular orbitals analysis and the calculated global reactivity descriptors of the respective GO-metal complexes revealed that all the GO-metal complexes have a smaller HOMO-LUMO gap (HLG) relative to that of pristine metal-free GO nanoparticle. This may indicate that although the GO-metal complexes are stable, they are less stable compared to metal-free GO nanoparticles. The negative values of the chemical potentials obtained for all the GO-metal complexes further confirm their stability. Our work differs from previous experimental studies in that those lacked details of the interaction mechanisms between GO, Pb and Cd, as well as previous theoretical studies which used limited numbers of parameters to characterise the GO-metal interactions. Rather, we present a set of parameters or descriptors which provide comprehensive physical and electronic characterisation of GO-metal systems as obtained via the DFT calculations. These parameters, along with those reported in previous studies, may find applications in rational design and high-throughput screening of graphene-based materials for water purification, as an example.

Boosting acetaminophen degradation in water by peracetic acid activation: A novel approach using chestnut shell-derived biochar at varied pyrolysis temperatures

In this study, biochar derived from chestnut shells was synthesized through pyrolysis at varying temperatures from 300 °C to 900 °C. The study unveiled that the pyrolysis temperature is pivotal in defining the physical and chemical attributes of biochar, notably its adsorption capabilities and its role in activating peracetic acid (PAA) for the efficient removal of acetaminophen (APAP) from aquatic environments. Notably, the biochar processed at 900 °C, referred to as CN900, demonstrated an exceptional adsorption efficiency of 55.8 mg g−1, significantly outperforming its counterparts produced at lower temperatures (CN300, CN500, and CN700). This enhanced performance of CN900 is attributed to its increased surface area, improved micro-porosity, and a greater abundance of oxygen-containing functional groups, which are a consequence of the elevated pyrolysis temperature. These oxygen-rich functional groups, such as carbonyls, play a crucial role in facilitating the decomposition of the O–O bond in PAA, leading to the generation of reactive oxygen species (ROS) through electron transfer mechanisms. This investigation contributes to the development of sustainable and cost-effective materials for water purification, underscoring the potential of chestnut shell-derived biochar as an efficient adsorbent and catalyst for PAA activation, thereby offering a viable solution for environmental cleanup efforts.

Flexible nanofiber composite solar evaporator for simultaneous interfacial evaporation and heavy metal ion adsorption

Solar driven interfacial evaporation (SDIE) is promising in harvesting fresh water because of its low cost, environmental friendless and sustainability; however, it is desirable but still difficult to achieve high efficiency heavy metal ion removal during SDIE. Here, we develop a superhydrophilic and stretchable nanofiber composite solar evaporator via carbon nanofiber (CNF) assembly on polymer fiber surface and then polydopamine (PDA) modification. The evaporation rate reaches as high as 1.456 kg m−2 h−1 with the evaporation efficiency of 91.40 %. The functional groups of PDA endow the nanofiber composite with good heavy metal ion adsorption performance that is proved to be an endothermic process, and SDIE can induce the increase of interface temperature and localized ion concentration and hence promote the Cr (VI) adsorption. One the other hand, NaCl ions are able to diffuse into body water without salt precipitation by virtue of powerful water transportation capability of the evaporation device. The dual Cr (VI) adsorption and NaCl ion diffusion channels ensure simultaneous and high efficiency Cr (VI) removal and seawater interface evaporation. SDIE accelerated heavy metal ion adsorption and the dual ion channel model provide inspiration to design multifunctional solar evaporator materials for waste water purification.

Carboxymethylcellulose sodium-derived carbon aerogels for solar-driven water purification

Recycling polluted water via different techniques has become one of the most feasible ways to solve the freshwater crisis. We describe a novel method to prepare reusable and efficient photothermal energy conversion materials for water purification. Using crosslinked xerogels as precursor, the porous and interconnected carboxymethylcellulose sodium-derived carbon aerogels (abbreviated as CCAs) with good hydrophilic performance and strong light absorption capability are firstly fabricated through pyrolysis. Photothermal measurement results show that CCA15 exhibit excellent solar steam generation rate of 2.31 kg m−2 h−1 with high light-to-vapor conversion efficiency of 95.9% under 1 sun illumination. In addition, the feasible application of CCA15 for efficient water purification under 1 sun irradiation using a homemade water treatment device has been demonstrated successfully. The as-prepared CCAs shown in here can be a continuable solution to mitigate the global freshwater crisis.

Three-dimensional graded porous structure and compressible KGM-GO/CS/SA composite aerogel spheres for efficient adsorption of antibiotics

The abuse of antibiotics led to significant environmental pollution through persistent residues in water bodies, posing severe risks to both ecological systems and human health. Addressing this issue, recent studies highlighted the potential of carbonaceous materials as effective adsorbents for removing antibiotics from water. Despite the proven potential of various carbonaceous materials in water purification, the application of three-dimensional porous microspherical aerogels as adsorbents presented a promising yet comparatively less discussed avenue in the quest for efficient antibiotic removal from aquatic environments.This work introduced a novel KGM-GO/CS/SA composite aerogel sphere, developed via a simple sol–gel and dripping method, using konjac glucomannan (KGM) as a cross-linking agent. We extensively analyzed its adsorption efficiency against common antibiotics such as tetracycline (TC), ofloxacin (OFL), and sulfadiazine (SDZ), revealing its rapid adsorption kinetics and high capacity. The aerogel's micro-morphology, characterized by a graded porous structure with abundant microporous channels and a low bulk density of 21.2 mg/cm3, along with its enhanced mechanical properties and thermal stability due to KGM cross-linking, signified its potential as a robust adsorbent. The surface functional groups facilitated diverse interaction mechanisms, including electrostatic attraction, hydrogen bonding, and π-π interactions, contributing to the adsorbent's high performance. Furthermore, the surface charge of the aerogel varied with pH, enhancing its electrostatic adsorption capabilities. The adsorption behavior was best described by the quasi-second-order and Langmuir models, with maximum capacities of 427.63 mg/g for OFL, 374.35 mg/g for TC, and 231.09 mg/g for SDZ, thereby offering a promising solution for antibiotic pollution remediation and illustrating the utility of carbon-based aerogel microspheres in environmental applications.

Enhanced interfacial interactions and enriched active sites in self-assembly amino-functionalized bacterial cellulose/MXene composite for wastewater treatment

With rapid industrialization and economic growth, the serious environmental pollution caused by heavy metals and dyes is a pressing issue to be solved. The efficient construction of enriched active sites and porous structures is the key to obtain water purification material for pollution removal. In this study, an efficient electrostatic self-assembly strategy to achieve amino-functionalized bacterial cellulose/Ti3C2Tx MXene (ABC/MX) composite with a 3D cross-linked porous structure has been proposed. Experimental characterization and theoretical calculations reveal that the successful incorporation of amino groups not only enhances the interfacial interactions between BC nanofibers and Ti3C2Tx nanosheets, but also increases the active sites available for adsorption. The results highlight that the ABC/MX composite exhibits exceptional removal efficiency, with maximum adsorption capacities of 200.7 mg/g for Cr(VI) and 1103.7 mg/g for Congo red (CR). In particular, it reveals that the multifaceted adsorption processes of Cr(VI) and CR involve electrostatic interactions, reduction reactions, chelation, and hydrogen bonding effects. These findings highlight a versatile strategy for synthesizing BC-based adsorbents with remarkable adsorption properties and are suitable for practical wastewater treatment applications.

Sunlight-activated Mo-doped La2CuO4/rGO perovskite oxide nanocomposite for photocatalytic treatment of diverse dyes pollutant

The pristine La2CuO4, Mo-doped, and rGO-supported nanocomposites were fabricated by a simple Pechini route. FTIR and XRD analysis confirmed the fabrication of the perovskite structure. The XRD results exhibit that the prepared products have no impurities and the dopant element is successfully incorporated into the perovskite material. FESEM images exhibit the morphology of synthesized perovskite material. EDX data showed the existence of lanthanum, copper, molybdenum, carbon, and oxygen in grown material. The energy band gap of the rGO-based composite was narrow compared with other samples. The photodegradation capability of the rGO-base catalyst was achieved 99.4 % (MB), 98.8 % (MO), 99.35 % (MR), 98.7 % (RhB), and 99.6 % (SO) in 75 min under natural sunlight illumination. The scavenger experiment revealed that superoxide and hydroxyl radicals are active species during the decolorization reaction. Moreover, this catalyst is stable for six cycles. The synthesized perovskite is an effective material for water purification and environmental remediation.

Geochemical Evaluation of Manganese Neutralization Sludge for Mn-Containing Mine Drainage Treatment

Conventional neutralization treatment for manganese (Mn)-bearing mine drainage provides a challenge of cost-efficiency, and new approaches should be explored for efficient removal of Mn. We focused on Mn neutralization sludge, a by-product of the Mn-bearing drainage treatment process, which was assumed to be useful as a water purification material. Mn and zinc (Zn) removal tests in simulated drainage were performed using Mn neutralization sludge, and the reaction mechanism was elucidated using geochemical modeling and X-ray absorption fine structure (XAFS) analysis. The results showed that the addition of sludge enabled to lower the Mn and Zn concentration below Japanese effluent standard (10 mg dm−3 for Mn; 2 mg dm−3 for Zn) within 1 h. Furthermore, heavy metal immobilization was achieved at neutral pH (7–8) with the sludge addition, while the conventional neutralization process without adding the sludge requires higher pH (>10) to lower Mn concentration. These removal behaviors were not explainable by considering only well-known phenomena: hydroxide precipitation, surface complexation reaction onto δ-MnO2, and autocatalytic Mn oxidation. Hence, we advanced the geochemical model for simulation, suggesting that a surface complexation reaction onto γ-MnOOH greatly contributed to the removal of Mn. Besides, Zn was calculated to be predominantly precipitated as ZnMn2O4. Solid residue analysis by XAFS measurement supported the result of above calculation, validating the reliability of the constructed geochemical model. Overall, we concluded that the advanced geochemical model would be useful in predicting the Mn and Zn behavior during mine drainage treatment with Mn neutralization sludge.Graphical abstract

Identification of the impact of electric pulse action on the disintegration of a natural mineral

The work is devoted to the study of the electric pulse disintegration of a natural mineral. The object of the study is the natural mineral quartzite of the Aktas deposit of the Republic of Kazakhstan. For the destruction and grinding of quartzite, a working cell of an electric pulse unit was developed. Electric pulse crushing is a modern technique for grinding a variety of materials, which provides the desired degree of grinding with a certain granulometric composition of the product and has a high ability of selective crushing. With the help of this technology, quartzite grinding was carried out with an increase in the capacity of capacitor banks from 0.25 mF to 1 mF, the pulse discharge voltage changed from 20 kV to 30 kV, the number of pulse discharges from 500 to 1,000, the inner diameter of the working cell from 60 mm to 80 mm. The results of the disintegration of a natural mineral by the electric pulse method allowed us to determine the degree of grinding of the finished product. The obtained results can be used in the study and optimization of the extraction of natural minerals, which is important for ensuring the sustainable use of natural resources and balanced economic development. Crushed quartzite is used in various industries, including the production of optical fibers, electronics and photovoltaic devices. A material with a particle diameter of 0.1 to 0.4 millimeters is used to create glass, ceramic and porcelain products, as well as insulation materials. Due to its homogeneous composition containing up to 98 % silicon oxide (SiO2) and excellent absorbent properties, quartz sand is also used as a filter material for water purification

Camel Dung-Derived Biochar for the Removal of Copper(II) and Chromium(III) Ions from Aqueous Solutions: Adsorption and Kinetics Studies.

This study explores an innovative approach to tackle the critical issue of heavy metal ion contamination in aqueous solutions through the utilization of camel dung-derived biochar. In the context of global environmental concerns and the adverse impacts of heavy metal pollution on ecosystems and human health, the investigation focuses on copper(II) and chromium(III) ions, which are among the most pervasive pollutants originating from industrial activities. The research revealed that camel dung-derived biochar exhibits exceptional potential for the removal of copper(II) and chromium(III) ions, with removal efficiencies of more than 90% and adsorption capacities of 23.20 and 23.36 mg/g, respectively. The adsorption processes followed second-order kinetics, and the data fitted both the Langmuir and Freundlich adsorption models. The underlying mechanisms governing this adsorption phenomenon seem to be grounded in complexation reactions, cation exchange, and cation-π interactions, underscoring the multifaceted nature of the interactions between the biochar and heavy metal ions. This research not only advances our understanding of sustainable materials for water purification but also harnesses the underutilized potential of camel dung as a valuable resource for environmental remediation, offering a promising avenue for addressing global water pollution challenges.

Enhanced removal of iron (Fe) and manganese (Mn) ions from contaminated water using graphene oxide-decorated polyethersulphone membranes: Synthesis and characterization.

This study addresses the urgent issue of water pollution caused by iron (Fe) and manganese (Mn) ions. It introduces an innovative approach using graphene oxide (GO) and GO-decorated polyethersulphone (PES) membranes to efficiently remove these ions from contaminated water. The process involves integrating GO into PES membranes to enhance their adsorption capacity. Characterization techniques, including scanning electron microscopy, Fourier-transform infrared, and contact angle measurements, were used to assess structural and surface properties. The modified membranes demonstrated significantly improved adsorption compared to pristine PES. Notably, they achieved over 94% removal of Mn2+ and 93.6% of Fe2+ in the first filtration cycle for water with an initial concentration of 100 ppm. Continuous filtration for up to five cycles maintained removal rates above 60%. This research advances water purification materials, offering a promising solution for heavy metal ion removal. GO-decorated PES membranes may find application in large-scale water treatment, addressing environmental and public health concerns.

Insights into uranium sequestration by coal fly-ash-derived zeolites: Understanding via wet chemistry, and advanced spectroscopies

The operation of nuclear power plants requires a supply of nuclear fuel where uranium plays a substantial role as a primary fissile material. Its extraction from U-bearing minerals and handling may cause a leakage of heavily toxic radioactive pollution, which ends up in water bodies and soil. Therefore, tackling U-contaminated water is crucial to preserve water integrity and quality. Zeolites are known as profound ion exchangers with great affinity towards cationic species present in polluted waters. Various zeolite synthesis routes have made this group of aluminosilicates even more promising to be applied as water purification materials. Here, the synthetic gismondite, faujasite, and Linde type-A zeolites from coal fly-ash were synthesized via tailored, coupled fusion-hydrothermal method and applied to remove aqueous uranium (primarily as 238U) under varying pH, time (sorption kinetics), and initial U concentrations (sorption isotherms). The maximum U uptake was observed for Na–P1 (GIS) zeolite, which equals 48.72 mg U/g, the highest reported value on maximum U adsorption capacity for zeolitic materials. The U adsorption kinetics showed that equilibrium is reached after approximately 3 h of adsorption and that the removal process follows a Freundlich isothermal model for all zeolites, thus preferential adsorption onto heterogeneous surfaces. Advanced spectroscopic studies, including laboratory-scale X-ray Photoelectron Spectroscopy with synchrotron light X-ray Absorption Near Edge Structure in High Energy Resolution Fluorescence Detection mode, revealed that at acidic pH, predominantly an ion exchange between Na+ ions with hexavalent uranyl species takes place. In contrast, in the neutral pH region, the U is immobilized via precipitation in the form of μm-scale mineral aggregates of Na-schoepite: Na[(UO2)4O2(OH)5](H2O)5↓. The outcomes of the research study has demonstrated that synthetic zeolites, obtained from industrial by-products such as coal fly-ash, can be successfully valorized to efficient U adsorbents while unveiling the insights to understand the zeolites/U interactions at the nanoscale level.

Surface defect and carbonyl engineering of CNTs via oxygen-plasma etching: Oriented production of singlet oxygen from peroxymonosulfate activation

A facile oxygen-plasma strategy was used to engineer carbon nanotubes (CNTs) surface with defects and carbonyl groups for organic water decontamination. The plasma-treated CNTs (E-CNTs) displayed a remarkable efficacy to catalyze peroxymonosulfate (PMS) activation for degrading electron-rich pollutants across a broad range of pH levels and under natural water conditions. Moreover, the kinetic constant for E-CNTs was found to be 4.1 times that of raw CNTs, attaining 97 % 2,4-DCP degradation in 20 min. The in situ capturing by electron paramagnetic resonance, chemical probing, and selectively scavenging tests collectively reveal that singlet oxygen (1O2) was the dominant reactive species with 54.9 % contribution to 2,4-DCP removal. The structure–activity relationship analysis and density functional theory (DFT) revealed that defects and carbonyl groups were the intrinsic catalytic sites for PMS activation. A comprehensive degradation pathway was proposed based on the properties of pollutant and degradation products from HPLC-MS and DFT calculations. Based on the ECOSAR analyses, the toxicity of the treated water (degradation intermediates) dramatically declined except for a polymerized bipolymer TP6 (m/z = 266.9). This article provides a novel method to create PMS-oriented active sites on carbon materials for selective singlet oxygen production and water purification.

Iron containing sludge-derived carbon towards efficient peroxymonosulfate activation: Active site synergy, performance and alternation mechanism

Converting industrial sludge into catalytic materials for water purification is a promising approach to simultaneously realize effective disposal of sludge and resource of water. However, manipulating the high efficiency remains a huge challenge due to the difficulty in the active sites control of the sludge. Herein, we proposed a constitutive modulation strategy by the combination of hydrothermal and pyrolysis (HTP) for the fabrication of defects-assistant Fe containing sludge-derived carbon catalysts on upgrading performance in peroxymonosulfate (PMS) activation for pollutant degradation. Adjustable defects on dyeing sludge-derived carbon catalysts (DSCC) were achieved by introducing oxygen or nitrogen functional precursors (hydroquinone or p-phenylenediamine) during hydrothermal processes and by further pyrolysis, where O was detrimental while N was beneficial to defect generation. Compared to the DSCC with less defects (DHSC-O), the defect-rich sample (DHSC-2N) exhibited superior catalytic performance of PMS activation for bisphenol A (BPA) elimination (k = 0.45 min−1, 2.52 times of DHSC-O), as well as 81.4% total organic carbon (TOC) removal. Meanwhile, the degradation capacity was verified in wide pH range (2.1–8.1) and various aqueous matrices, reflecting the excellent adaptability and anti-interference performance. Furthermore, the continuous-flow experiments on industrial wastewater showed synchronous BPA and chemical oxygen demand (COD) removal, implying great potential for practical application. Solid electron paramagnetic resonance (EPR) and 57Fe Mösssbauer spectra analysis indicated that the defects acted as secondary active sites for Fe sites, which were beneficial to accelerating the electron transfer process. The only Fe active sites preferred the radical pathway. The controllable reaction tendency provides possibilities for the on-demand design of sludge-based catalysts to meet the requirements of practical wastewater treatment under Fenton-like reaction.