Search Results (360)

Malachite green (MG), a triarylmethane dye extensively used in the textile and aquaculture industries, is a persistent aquatic contaminant with documented carcinogenic, mutagenic, and teratogenic effects even at trace concentrations. In the present work, a natural, low-cost Serpentine clay was surface-modified with copper oxide nanoparticles generated in situ through a green, lemon-extract-mediated reduction of copper nitrate, yielding a novel SER/CuO nanocomposite. The as-prepared adsorbent was characterized by FTIR, XRD, BET, and SEM to confirm the successful anchoring of CuO nanoparticles onto the Serpentine lattice. Batch adsorption experiments demonstrated that the removal of MG was governed by solution pH, adsorbent dose, contact time, and initial dye concentration, with maximum uptake obtained close to neutral pH, consistent with the point of zero charge (pH_pzc = 7.6) of the composite relative to the pKa (6.9) of the dye. Equilibrium data were described comparably well by the Langmuir and Freundlich isotherms at 25 and 55 °C, with a maximum monolayer capacity of 279.06 mg g⁻¹ at 25 °C, while kinetic analysis showed the closest statistical agreement with the Elovich model, pointing to an energetically heterogeneous, chemisorption-assisted process supported by a three-stage intraparticle-diffusion profile. The individual and combined effects of solution pH, adsorbent dose, and contact time on removal efficiency were systematically evaluated using a one-factor-at-a-time approach. Thermodynamic estimation from the two-temperature Langmuir constants indicated a spontaneous and exothermic, and entropy-favored adsorption process. The spent adsorbent was regenerated using dilute hydrochloric acid and retained appreciable efficiency over successive cycles. Comparison to previously reported adsorbents supported the competitiveness of SER/CuO in terms of capacity, cost, and simplicity of preparation, and a techno-economic appraisal supported the feasibility of scale-up. As a waste-valorization step, both the bare SER/CuO adsorbent and its MG-loaded form were evaluated as electrode materials for the urea oxidation reaction: MG loading raised the anodic current density from 143.10 to 176.46 mA cm⁻² at 1.0 M urea, nearly doubled the electrochemically active surface area (7.34 to 14.41 cm²), and lowered the charge-transfer resistance, while sustaining a higher stable current density (111 vs. 81 mA cm⁻²) over 3600 s of continuous operation demonstrating a promising route for coupling water remediation with energy recovery. Full article

Adsorptive interactions between adsorbents and toxic contaminants are significantly exploited to the advantage of water treatment goals. In this study, adsorptive interactions in aqueous solution between Pb (II) ions and a lowly toxic and structurally robust metal–organic framework, zinc-trimesate framework (Zn-H₃btc), were evaluated using thermodynamic, equilibrium and kinetic models to establish the capacity of the material to adsorb Pb (II) ions from water. Zn-H₃btc was synthesized by refluxing mixtures of zinc nitrate and trimesic acid in DMF solvent and characterized using FTIR, SEM, EDS, PXRD, TGA and DTG methods. Adsorption experiments were carried out on the basis of variation in initial concentration, contact time, pH, adsorbent dosage, and temperature. Langmuir isotherm was the best-fitting isotherm. The maximum monolayer adsorption capacity of Zn-H₃btc was 54.05 mg/g. Kinetic studies revealed a pseudo-second-order controlled adsorption process, and hence a chemisorption mechanism. The thermodynamic parameters, Gibbs free energy, ΔG, activation energy, E_a, sticking probability, S*, and isosteric heat of adsorption ΔH_x, indicated that the adsorption process was spontaneous and required a minimal energy barrier; however, it had a fairly large amount of isosteric heat (133.39 kJ/mol) released. The findings confirm the applicability of Zn-H₃btc as an adsorbent of Pb (II) ions in aqueous solution. Full article

This study focuses on the shaping of ZSM–5-based granules using conventional pseudoboehmite as well as aluminum hydroxynitrate precursors obtained by partial thermal treatment of Al(NO₃)₃·9H₂O. The starting materials and nitrate-derived precursors were characterized by X-ray diffraction, thermal analysis, infrared spectroscopy, scanning electron microscopy, and low-temperature nitrogen adsorption. Model pseudoboehmite systems were used to evaluate the effects of moisture, peptization equivalent, and HNO₃ concentration in the initial liquid portion on pore volume, apparent density, shrinkage, and axial and radial crushing strength. Acid peptization showed a strongly non-linear effect: small HNO₃ additions increased strength and densification, whereas excess acid promoted structural heterogeneity and granule disintegration during thermal treatment. Even at constant moisture and total acid dosage, strength depended markedly on the initial peptizer concentration. In unpeptized ZSM–5/pseudoboehmite composites, increasing zeolite content reduced pore volume but increased density and strength, indicating formation of a more compact framework. Aluminum hydroxynitrate precursors enabled effective shaping of ZSM–5-containing pastes, demonstrating their potential as alternative binder precursors, while the optimized pseudoboehmite systems provided the most favorable overall balance between porosity and mechanical stability. Full article

Planted and unplanted recirculating constructed wetland mesocosms maintained under non-aerated (reducing) and aerated (oxidizing) conditions were compared in their ability to remove 1 mg/L As(V) from simulated domestic wastewater over a 33-week period. Each week, one day prior to the addition of arsenic, non-aerated mesocosms removed 70% of the nitrate and 95% of the organic carbon likely through denitrification while aerated mesocosms removed organic carbon only (97%). Upon arsenic addition and treatment for the remainder of the week, non-aerated mesocosms removed more arsenic (72%) than aerated mesocosms (43%). For the first time in the literature, we estimated the proportion of arsenic found in biofilms detached from gravel and incorporated this aspect into mass balance calculations. We discovered that biofilms from non-aerated mesocosms contained a higher proportion of arsenic (28%) than biofilms from aerated mesocosms (5%). Plants from both types of mesocosms removed a negligible amount of arsenic (<0.41%). Through X-ray fluorescence (XRF) analysis, it was discovered that biofilms from non-aerated mesocosms had the highest iron concentrations (35,000 mg/kg), and this iron was identified as pyrite (2–15 wt%) through X-ray diffraction (XRD) analysis. The iron concentration of aerated biofilms was no different from that found in clean gravels (17,500 mg/kg), and no iron minerals were detectable in these samples using XRD analysis. Although some of the arsenic removal in both types of wetlands was thought to be attributable to adsorption onto substrates and biofilms, as well as uptake into biofilms, removal of arsenic in the non-aerated mesocosms was likely enhanced by the presence of pyrite because pyrite can adsorb arsenic directly or indirectly through the formation of iron oxides that can adsorb or coprecipitate with the iron oxides. Full article

To address the challenges of weak NO₃⁻ adsorption, insufficient active hydrogen supply, and facile desorption of NO₂⁻ intermediates in neutral electrocatalytic nitrate reduction reaction (NO₃RR), this study employs laser nano-welding technology to fabricate a Ru/WO₃ heterojunction, and constructs a Ru/WO₃/Cu(OH)₂/FC spatially confined electrode using Cu(OH)₂ nanorod arrays as the support. Laser welding achieves metallurgical-grade bonding between Ru and WO₃ while retaining oxygen vacancies in WO₃. Cu(OH)₂ promotes NO₃⁻ adsorption via electrostatic and Lewis acid interactions, and its nanorod array structure confines NO₂⁻ intermediates. In 0.5 M K₂SO₄ + 50 mM KNO₃ electrolyte, the electrode delivers an ammonia yield rate of 16.1 mg h⁻¹ cm⁻² and a Faradaic efficiency of 75.8% at −0.8 V vs. RHE, outperforming control groups. Potential-dependent electrochemical impedance spectroscopy (EIS) confirms that spatial confinement suppresses NO₂⁻ accumulation and optimizes interfacial charge transfer kinetics, providing a new strategy for electrode design in neutral NO₃RR. Full article

Large volumes of solid waste are produced by the winemaking sector, which could be utilised as adsorbents to retain contaminants, providing a beneficial approach in terms of economic recovery and sustainability. The adsorption of nitrate onto biochar produced from grape pomace has not received enough attention, even though biochar-based materials have been thoroughly studied for water treatment applications. This study aims to fill the knowledge gap by assessing a low-cost mildly carbonized biochar derived from winery residues for nitrate retention and optimising the nitrate retention procedures by comprehensive physicochemical characterisation. The mildly carbonized biochar prepared from grape pomace collected from the Dealu Mare wine region (Romania) was characterized using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM–EDX), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), and thermogravimetric and derivative thermogravimetric (TGA/DTG) analyses. Results revealed a structure enriched with oxygen-containing functional groups that promote nitrate retention through combined physical adsorption and electrostatic interactions. Surface analyses after adsorption confirmed the successful immobilization of nitrate species on the biochar matrix. The adsorption performance was improved by Response Surface Methodology (RSM) method using a Central Composite Design (CCD), studying the influences of the following parameters: solution pH, adsorbent weight, nitrate concentration and time. Among all variables, pH was identified as the dominant factor controlling adsorption efficiency, reflecting the key role of surface charge interactions. The optimized conditions (175 mg/L nitrate, pH 6, 0.3 g adsorbent dosage, and 94 min contact time) resulted in a maximum nitrate removal efficiency (RE) of 86.69%, while the predictive model exhibited excellent accuracy (R²_adj = 0.985). The findings demonstrate that mildly carbonized grape pomace biochar can achieve competitive nitrate removal without chemical surface modification, offering a more sustainable and economically attractive alternative to conventionally biochars. The research highlights that selecting feedstock and utilizing intrinsic surface functionality can create efficient nitrate adsorbents from agro-industrial residues. Full article

Nitrites and nitrates are admitted into the body through the consumption of various foods, primarily cured meat products. These nitrites and nitrates are precursors of reactive nitrogen species NO and NO₂, which, in excess, promote nitrosative stress. Attempts have been made to combat oxidative and nitrosative stress through C₆₀ fullerenols in animal models. Furthermore, experimental and theoretical studies have shown that the use of carbon nanomaterials such as defective or doped graphene and C₆₀ metallofullerenes facilitates the capture of NO_x pollutants contained in the air. This leads us to propose that the inclusion of metals in C₆₀ fullerenols may have the potential to capture these reactive nitrogen species and be considered in nitrosative stress tests in animal models. Alternatively, viewed from another perspective, a certain grade of hydroxylation of metallofullerenes could enhance the capture of atmospheric nitrogen pollutants. Therefore, Li, Ca and Y metals were included in C₆₀ fullerenols at different coating grades. Using density functional theory (DFT), we analyzed the antiradical character of these metallofullerenols, and the adsorption energies of the free radicals (NO_x) were calculated to evaluate the ability of these metallofullerenols to adsorb these nitrogen species. Although both fullerenols and endohedral metallofullerenes have individually shown promise as radical scavengers, a systematic understanding of how the encapsulated metal and the grade of hydroxylation jointly govern the capture of nitrogen species is still lacking. In particular, it remains unclear whether increasing the number of hydroxyl groups monotonically enhances the capture capacity or whether optimal combinations of metal identity and surface functionalization exist. Addressing this gap is crucial, since excessive hydroxylation may alter the electronic structure, stability, and mechanism of interaction with NO_x radicals, potentially compromising capture capacity. Therefore, a rational evaluation that simultaneously considers electronic donor–acceptor properties, local reactivity, and adsorption thermodynamics is required to identify metallofullerenols with possible potential to sense or scavenge NO_x. Full article

The large-scale production and utilization of nitrogen-containing compounds have greatly promoted the development of modern agriculture and the chemical industry, but have also resulted in increasingly severe nitrate contamination and an imbalance of the nitrogen cycle. The efficient conversion of nitrate into value-added ammonia not only contributes to pollutant remediation but also provides a promising route for green ammonia synthesis. Owing to its mild reaction conditions, potentially lower environmental impact, and compatibility with renewable electricity, electrocatalytic nitrate reduction to ammonia has attracted considerable attention in recent years. This process involves a multielectron transfer process involving numerous intermediate transformations, and its catalytic performance largely depends on the adsorption and conversion of key intermediates on the catalyst surface, as well as the suppression of the competing hydrogen evolution reaction. This review systematically summarizes recent advances in electrocatalytic nitrate reduction to ammonia, with emphasis on the reaction mechanisms and major reaction pathways, as well as the design strategies, structure–activity relationships, and performance enhancement mechanisms of metal-based, carbon-based, and composite catalysts. In addition, the main challenges in this field, including product selectivity, mass transport, in-situ mechanistic characterization, and long-term stability, are discussed. Finally, the construction of highly efficient catalytic systems and key directions for future research are outlined, with particular emphasis on nitrate valorization and sustainable ammonia synthesis. Full article

Biochar has attracted increasing attention for aquatic pollution control, particularly due to its capacity to accelerate the rate-limiting steps of denitrification in wastewater treatment. While early research primarily focused on the adsorption capacity of biochar, recent studies have increasingly investigated its role as a redox-active mediator that facilitates electron transfer. This review critically synthesizes the multifaceted mechanisms of biochar-enhanced denitrification, establishing a link between synthesis parameters (feedstock, pyrolysis kinetics) and physicochemical functionalities (pore architecture, redox-active functional groups). Specifically, we elucidate how precise regulation of pyrolysis temperature dictates the dominant electron transfer pathway: low-temperature biochar (<500 °C) facilitates electron shuttling via oxygen-containing functional groups (e.g., quinone moieties), whereas high-temperature biochar (>700 °C) promotes direct interspecies electron transfer (DIET) through graphitic conduction. We systematically decouple biochar-mediated electron transfer into three pathways: functional group-driven shuttling, solid-state conductive matrix transfer via conjugated π-electrons, and material-assisted DIET. Crucially, we emphasize that validating true DIET requires direct biological evidence of electroactive machinery. Furthermore, the review details how biochar modulates the biological microenvironment, upregulating key denitrification genes (narG, nirS/K, nosZ) and enriching functional microbial consortia. By integrating advances in surface modification—such as heteroatom doping and metal loading—we propose strategies to engineer biochar for optimized nitrate-to-nitrogen conversion. Future perspectives underscore the need for balancing electron-donating capacity with structural stability, developing low-energy functionalization techniques, and conducting life-cycle assessments to facilitate the scale-up of sustainable, high-efficiency nitrogen removal systems. Full article

Oilfield-produced water contains petroleum hydrocarbons, suspended solids, salts and other refractory constituents that challenge conventional biological treatment. Suspended activated sludge systems can suffer from microbial washout, poor retention of slow-growing functional microorganisms and unstable settling, whereas conventional ceramic biofilm packings often provide limited surface area and slow biofilm start-up. Here, a modified polyurethane biosponge was evaluated as a three-dimensional carrier for immobilized microbial growth during the treatment of real oilfield produced water. Three parallel systems were compared under identical start-up and operating conditions: suspended activated sludge without a carrier, Raschig ring-packed biofilm reactors, and the biosponge-based composite system. The biosponge system developed a visible and stable biofilm within 7 days, whereas the Raschig ring system showed only sparse and uneven biofilm coverage. During an 8-day treatment test with real produced water, the biosponge system decreased the COD concentration from 800 to 13 mg L⁻¹ in the aerobic zone and from 1500 to 16 mg L⁻¹ in the anoxic zone, corresponding to removal efficiencies of 98.4% and 98.9%, respectively. In contrast, the activated sludge and Raschig ring systems showed much lower COD removal under the same test period. 16S rRNA gene sequencing indicated that the biosponge selectively enriched petroleum hydrocarbon-associated genera, including Sphingopyxis, Achromobacter and Gordonia, in the aerobic zone, together with fermentative and anaerobic genera such as Dysgonomonas and Clostridium in the anoxic zone. PICRUSt2-based functional prediction further suggested the coexistence of aerobic hydrocarbon degradation, chemoheterotrophy, fermentation and nitrate respiration potentials. These results indicate that the modified polyurethane biosponge provides a favorable carrier for rapid biofilm establishment and short-term removal of organic pollutants from oilfield produced water. Further long-term operation, adsorption controls and direct functional gene validation are recommended to confirm the engineering robustness and degradation mechanisms of the system. The system also avoided sludge bulking and maintained short-term stability, providing a promising low-cost strategy for treating high-salinity refractory oilfield produced water. Full article

Groundwater resources in semi-arid regions are increasingly threatened by agricultural intensification, irrigation expansion, and climate variability. This study investigates the influence of irrigation practices on groundwater recharge and quality degradation in the semi-arid Regueb Basin, Central Tunisia, using an integrated framework combining hydrochemical analysis, irrigation water quality indices, GIS-based spatial modeling, and explainable machine learning (XAI). Thirty groundwater samples were analyzed for major physicochemical parameters and irrigation suitability indicators, including Electrical Conductivity (EC), Total Dissolved Solids (TDS), Sodium Adsorption Ratio (SAR), sodium percentage (%Na), and Irrigation Water Quality Index (IWQI). Hydrochemical facies are dominated by Ca–Mg–Cl, Na–Cl, and Ca–Mg–SO₄ water types, reflecting the combined effects of evaporite dissolution, water–rock interaction, evaporation, and irrigation return flow. Groundwater salinity is generally high, with EC values ranging from 1490 to 8710 µS/cm, while nitrate concentrations frequently exceed the World Health Organization guideline value of 50 mg/L in intensively cultivated zones, indicating significant anthropogenic contamination linked to fertilizer leaching and irrigation practices. GIS-based recharge assessment indicates that irrigation return flow may represent an important component of effective recharge in cultivated areas under semi-arid conditions while simultaneously contributing to salinization and nutrient accumulation within the aquifer system. However, quantitative partitioning of recharge sources requires further investigation using tracer-based approaches and numerical modeling. More than 40% of groundwater samples were classified as unsuitable for irrigation because of elevated salinity and sodicity hazards. To explore the relationships among irrigation water quality indicators, several machine-learning algorithms were evaluated for IWQI estimation and interpretation. Linear Regression achieved the highest performance for IWQI estimation (R² = 0.9839), reflecting the strong internal relationships among irrigation water quality indicators. SHapley Additive exPlanations (SHAP) analysis identified Residual Sodium Carbonate (RSC) as the most influential parameter controlling irrigation water quality. The results highlight the dual role of irrigation as both a recharge-enhancing mechanism and a driver of groundwater degradation. This study provides an integrated hydrochemical–GIS–XAI framework for identifying vulnerable zones and supporting sustainable groundwater management strategies in semi-arid agricultural regions. Full article

Two natural materials, pozzolan from Aguelmous (Middle Atlas, Morocco) and local gravel (3–6 mm), were selected and compared as permeable layers in a multi-soil layering (MSL) system treating domestic wastewater. This comparison was motivated by the need to evaluate a widely used conventional material in Morocco (gravel) against a highly porous volcanic pozzolan expected to improve pollutant removal due to its superior structural and physicochemical properties. The study combined physicochemical characterization, adsorption experiments using methylene blue (MB) and methyl orange (MO), and pilot-scale multi-soil layering (MSL) system tests under vertical-flow conditions. Pozzolan exhibited a highly porous structure with a specific surface area of 13.77 m²·${\mathrm{g}}^{-1}$ and a total porosity of 70.12%, compared with 1.92 m²·${\mathrm{g}}^{-1}$ and 45.49% for gravel, respectively. These properties resulted in higher adsorption performance, with MB removal efficiencies of 66.60% for pozzolan versus 45.35% for gravel at 16.5 mg·${\mathrm{L}}^{-1},$ and MO removal efficiencies of 69.12% versus 58.55% at 10 mg·${\mathrm{L}}^{-1}$. Correspondingly, pozzolan showed higher adsorption capacities for MB (9.976 mg·g⁻¹) and MO (1.534 mg·g⁻¹) than gravel (0.829 and 0.750 mg·g⁻¹, respectively). In pilot-scale operation, pozzolan-based filters achieved higher removal efficiencies for BOD₅ (82.01%), COD (86.14%), ammoniacal nitrogen (89.48%), and total phosphorus (66.30%) compared with gravel (75.56%, 78.24%, 61.56%, and 50.42%, respectively). The enhanced ammoniacal nitrogen removal in filter F2 (6–15 mm) is attributed to favorable aerobic conditions within the system, which likely promoted nitrification due to improved oxygen availability. However, the absence of sufficient anoxic zones limited denitrification, leading to nitrate (${\mathrm{N}\mathrm{O}}_3^{-}$) accumulation. Overall, the results indicate that natural pozzolan is a highly suitable permeable material for enhanced pollutant removal, making it a promising alternative to conventional gravel in decentralized MSL wastewater treatment systems. Full article

This study examined the removal of toxic heavy metals Pb²⁺ and As⁵⁺ from wastewaters by applying a waste nut biomass for adsorption. The waste material was steam-activated and further modified with zinc nitrate tetrahydrate to improve its affinity for arsenate. The adsorption performance was evaluated across a range of contact times, sorbent dosages, initial metal concentrations, and pH levels, for both single-metal and mixed-metal systems. When the raw material was modified by Zn, the maximum uptake of As⁵⁺ reached a value of 51 mg/g, at a sorbent dosage of 2 g/L. In binary metal solutions, the biochar exhibited maximum capacities of 25.5 mg/g for Pb²⁺ and 48.5 mg/g for As⁵⁺, indicating minimal competition between the two ions for adsorption sites on the biochar surface. Full article

Lead (Pb) is a persistent and highly toxic heavy metal that poses significant ecological and human health risks due to its high bioaccumulation potential. In this study, nitrogen-doped biochar (NBC) was synthesized from straw-derived biochar via ball-milling and ammonium nitrate modification to remediate Pb-contaminated soil. Batch adsorption experiments demonstrated that the adsorption process was best described by the Langmuir isotherm model, indicating monolayer adsorption. X-ray photoelectron spectroscopy (XPS) revealed that Pb(II) immobilization by NBC occurred through multiple mechanisms, primarily precipitation and complexation with hydroxyl and pyrrolic-N functional groups. Subsequent pot experiments confirmed that NBC outperformed pristine biochar (BC) in reducing Pb bioavailability. This superior performance was attributed to the ability of NBC to increase soil pore water pH and significantly decrease soil redox potential (Eh). Moreover, compared to the control, a 5% NBC treatment (NBC2) significantly increased soil organic matter (SOM) by 136.24% while concurrently increasing soil available nitrogen (SAN), phosphorus (SAP), and potassium (SAK) by 46.91%, 75.72%, and 42.79%, respectively. Microbiological analyses indicated that NBC application enhanced soil alpha diversity (Chao1, ACE, and Shannon indices) and enriched beneficial bacterial phyla, such as Proteobacteria and Firmicutes. Random forest analysis identified the acid-soluble Pb fraction and SOM as the main drivers of bacterial operational taxonomic unit (OTU) composition. Specifically, NBC increased the relative abundance of the family Hungateiclostridiaceae, which may promote soil sulfide production and facilitate the precipitation of Pb into highly insoluble forms, further reducing its mobility and toxicity. Collectively, these findings demonstrate that NBC is a promising soil amendment that leverages both physicochemical and microbial pathways to immobilize Pb, mitigate environmental toxicity, and restore soil ecological health. Full article

This research investigates cobalt-based and iron-based coordination polymers as advanced adsorbents for removing nitrate from water, addressing the increasing demand for effective and customizable treatment materials. Both coordination polymers were synthesized through solvothermal methods using terephthalic acid as the organic linker and were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), which verified their crystalline, porous structures and uniform metal dispersion; Fourier-transform infrared spectroscopy (FTIR) was used to analyze surface characteristic functional groups of the samples before and after adsorption. Batch adsorption tests combined with response surface methodology (RSM), based on a Box–Behnken (BBD), were employed to optimize key operating conditions, including adsorbent dose (0.1–0.5 g/L), pH (3–7), and temperature (25–45 °C). Under optimal conditions (pH 3–5, 0.3 g/L, 30–35 °C), the Co-coordination polymer achieved a maximum nitrate removal of 54.1% and an adsorption capacity of 212.8 mg/g, while the Fe-coordination polymer reached 30.5% removal with a capacity of 35.0 mg/g. Kinetic studies were well fitted by the pseudo-second-order (PSO) model for the Co-coordination polymer (R² = 0.992–0.997), indicating chemisorption control, whereas the Fe-coordination polymer exhibited diffusion-driven behavior. The equilibrium data fit the Langmuir model well for both, confirming monolayer adsorption. The findings suggest that the Co-coordination polymer provides superior nitrate removal owing to stronger metal–anion interactions, whereas the Fe-coordination polymer offers more stable but lower adsorption capacity. Full article