Search Results (177)

It is understood that 4-nitrophenol (4-NP) and its derivatives/isomers, such as m-NP and o-NP, are considered toxic nitroaromatic pollutants that pose health risks for human beings and have negative impacts on the environment. Therefore, monitoring of 4-NP is of particular importance to avoid the negative impacts of these environmental pollutants on aquatic life and human health. Electrochemical sensors have emerged as the most promising next-generation technology for the detection of environmental pollutants. The electrochemical method has been extensively used for the detection of 4-NP, p-NP, etc., which has delivered an interesting electrochemical performance. This review provides an overview of the advances in electrode modifiers designed for the electrochemical detection of 4-NP and its isomers. This review includes the use of carbon-based materials, metal oxides, metal sulfides, metal-organic-frameworks (MOFs), conducting polymers, MXenes, covalent organic frameworks (COF), and composites for the development of 4-NP electrochemical sensors. Various electrochemical techniques, such as differential pulse voltammetry, square wave voltammetry, linear sweep voltammetry, cyclic voltammetry (CV), electrochemical impedance spectroscopy, and amperometry, are discussed for the detection of 4-NP and other isomers. Full article

Understanding how the surface charge environment governs pollutant–catalyst interactions is essential for designing efficient photocatalysts. In this study, ZnO–CeO₂–WO₃ composite materials were synthesized through a simplex-centroid mixture design to evaluate their photocatalytic activity toward the degradation of 4-nitrophenol (4-NPOH) under UV irradiation. The materials were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), UV–Vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL), nitrogen adsorption–desorption (BET/DFT) and scanning electron microscopy (SEM). Photocatalytic experiments were conducted without pH adjustment to analyze the intrinsic behavior of each oxide and their mixtures. The acid–base equilibrium of 4-NPOH (pK_a = 7.2) allowed evaluating its deprotonation to 4-nitrophenolate (4-NP⁻) and its interaction with the catalyst surface, which depends on the point of zero charge (pH_Pzc) of ZnO, CeO₂, and WO₃. The Zn–W binary system (ZnWO₄ phase) exhibited the highest activity, achieving 81% degradation efficiency and the largest apparent rate constant (k = 5.1 × 10⁻³ min⁻¹). However, a 51% decrease in activity was observed after three reuse cycles, attributed to WO₃ leaching induced by the interaction between 4-NPO⁻ and zinc tungstate hydroxide (Zn[W(OH)₈]). This work establishes a direct correlation between surface charge, pollutant speciation, and photocatalytic performance, providing a mechanistic framework for understanding pH-dependent degradation processes over multicomponent oxide composites. Full article

This study quantifies radical pathways and the influence of process variables in a 425 kHz sonoreactor through a coupled calorimetric and multidosimetric approach during Sunset Yellow FCF degradation. Reactive oxygen species were mapped with four complementary dosimeters. Potassium iodide (KI) tracked interfacial hydroxyl radicals (^•OH). KI with ammonium heptamolybdate (AHM) captured ^•OH radicals together with hydrogen peroxide (H₂O₂). Bulk H₂O₂ accumulation integrated the recombination branch. Hydroxylation of 4-nitrophenol to 4-nitrocatechol acted as a selective near-interface ^•OH probe. Calorimetry showed that acoustic power density increased with set power and decreased with liquid height. All four dosimeters rose coherently with this variable, indicating that stronger driving elevated ^•OH generation while channeling a larger fraction into H₂O₂ through recombination. Process studies linked energy delivery to performance across operating conditions. Higher power accelerated pseudo-first order dye decay. Increasing initial dye concentration reduced fractional removal at fixed power, consistent with a radical-limited regime. Acidic media enhanced degradation by maintaining a stronger hydroxyl radical to water redox couple and by improving H₂O₂ persistence. Near neutral and alkaline media exhibited carbonate and bicarbonate scavenging of hydroxyl radicals and faster peroxide loss. Dissolved gas identity strongly modulated activity. Oxygen and argon outperformed air and carbon dioxide due to the combined thermophysical and chemical roles of the bubble gas. The calorimetry anchored and multidosimetric protocol provides a general route to compare reactors, optimize conditions, and support scale-up based on delivered energy density. Ultrasonication-driven degradation is a robust, practical technology for advanced treatment of dye-laden waters. Full article

The pervasive discharge of synthetic dyes into aquatic ecosystems poses a significant threat due to their chemical stability, low biodegradability, and carcinogenicity. Conventional dye remediation methods—such as biological treatments, coagulation, and adsorption—have demonstrated limited efficiency and poor reusability, particularly against resilient azo dyes. Cerium oxide (CeO₂) nanoparticles have gained traction as photocatalysts owing to their redox-active surfaces and oxygen storage capabilities; however, issues like particle agglomeration and rapid charge recombination restrict their catalytic performance. To address these challenges, this study presents the novel synthesis of a graphene oxide–cerium oxide (GO-CeO₂) nanocomposite via a facile in situ hydrothermal approach, using graphite from lead pencils as a sustainable precursor. The composite was structurally characterized using UV–visible spectroscopy, XRD, FTIR, and TEM. The GO matrix not only facilitates uniform dispersion of CeO₂ nanoparticles but also enhances interfacial electron mobility and active site availability. The nanocomposite demonstrated exceptional photocatalytic degradation efficiencies for methyl orange (94%), methyl red (98%), congo red (96%), and 4-nitrophenol (85.6%) under sunlight irradiation, with first-order rate constants significantly exceeding those of pure CeO₂. Notably, GO–CeO₂ retained strong catalytic activity over four degradation cycles, confirming its recyclability and structural stability. Total organic carbon (TOC) analysis revealed 79% mineralization of methyl orange, outperforming CeO₂ (45%), indicating near-complete conversion into benign byproducts. This work contributes a scalable, low-cost, and highly active heterogeneous photocatalyst for wastewater treatment, combining green synthesis principles with improved photodegradation kinetics. Its modular architecture and reusability make it a promising candidate for future environmental remediation technologies and integrated photocatalytic systems. Full article

In this work, two novel nanoscale zero-valent iron (nZVI) composites (nanoscale zero-valent iron and copper-intercalated montmorillonite (MMT-nFe⁰/Cu⁰) and carbon microsphere-supported sulfurized nanoscale zero-valent iron (CMS@S-nFe⁰)) were used to treat soil contaminated with both Cr(VI) and p-nitrophenol (PNP), and added persulfate (PMS). Experiments found that the pollutant removal effect has a great relationship with the ratio of water to soil, the amount of catalyst, the amount of PMS, and the pH value. When the conditions are adjusted to the best (water–soil = 2:1, catalyst 30 g/kg, PMS 15 g/kg, pH 7–9), both materials fix Cr(VI) well and decompose PNP. The removal rates of Cr(VI) and PNP by the MMT-nFe⁰/Cu⁰ system are 90.4% and 72.6%, respectively, while the CMS@ S-nFe⁰ system is even more severe, reaching 94.8% and 81.3%. Soil column leaching experiments also proved that the fixation effect of Cr can last for a long time and PNP can be effectively decomposed. Through detection methods such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), we found that Cr(VI) was effectively reduced to Cr(III) by Fe⁰ and Fe²⁺ ions and subsequently transformed into stable FeCr₂O₄ spinel oxides, and the groups produced after the decomposition of PNP could also help fix the metal. This work provides a way to simultaneously treat Cr(VI) and PNP pollution, and also allows the use of multifunctional nZVI composites in complex soil environments. Full article

Environmental pollution and sustainability issues require environmentally friendly solutions. In this study, we synthesized copper oxide nanoparticles (CuO NPs) using a sol––gel method with Croton macrostachyus bark extract for application in environmental remediation and as an antimicrobial agent. The uncalcined CuO NPs (200 mg/mL) demonstrated strong antimicrobial activity, with inhibition zones of 22 ± 1.3 mm against Staphylococcus aureus and 11 ± 0.7 mm against Escherichia coli. Moreover, the nanoparticles efficiently catalyzed the reduction of 4-nitrophenol, achieving 98.79% degradation within 8 min (K_app = 0.507 min⁻¹). These findings show that CuO NPs synthesized from the extract of Croton macrostachyus provide a sustainable and efficient approach for addressing both environmental pollution and antibacterial resistance. Full article

Titanium-containing nanoparticles have emerged as materials of significant technological importance due to their multifunctional properties and excellent performance. With their expanding applications, the amount of TiO₂ nanoparticles (TNPs) being released into the soil environment has increased significantly. This review addresses the gap in current research, which has predominantly focused on the environmental behavior of TNPs in aquatic systems while lacking systematic integration of the synergetic mechanism of adsorption–transformation–ecological effects in soil systems and its guiding value for practical applications. It deeply reveals the interaction mechanisms between TNPs and environmental pollutants. TNPs exhibit outstanding adsorption performance towards environmental pollutants such as heavy metals and organic compounds. Specifically, the maximum adsorption capacities of titanate nanowhiskers for the heavy metal ions Cu(II), Pb(II), and Cr(III) are 143.9 mg·g⁻¹, 384.6 mg·g⁻¹, and 190.8 mg·g⁻¹, respectively. Additionally, 1-hydroxydinaphthoic acid surface-modified nano-TiO₂ exhibits an adsorption rate of up to 98.6% for p-nitrophenol, with an enrichment factor of 50-fold. The transformation process of TNPs after pollutant adsorption profoundly affects their environmental fate, among which pH is a critical controlling factor: when the environmental pH is close to the point of zero charge (pHpzc = 5.88), TNPs exhibit significant aggregation behavior and macroscopic sedimentation. Meanwhile, factors such as soil solution chemistry, dissolved organic matter, and microbial activities collectively regulate the aggregation, aging, and chemical/biological transformation of TNPs. In the soil ecosystem, TNPs can exert both beneficial and detrimental impacts on various soil organisms, including bacteria, plants, nematodes, and earthworms. The beneficial effects include alleviating heavy metal stress, serving as a nano-fertilizer to supply titanium elements, and acting as a nano-pesticide to enhance plants’ antiviral capabilities. However, excessively high concentrations of TiO₂ can stimulate plants, induce oxidative stress damage, and impair plant growth. This review also highlights promising research directions for future studies, including the development of safer-by-design TNPs, strategic surface modifications to enhance functionality and reduce risks, and a deeper understanding of TNP–soil microbiome interactions. These avenues are crucial for guiding the sustainable application of TNPs in soil environments. Full article

Addressing the urgent need for robust and sustainable catalysts to detoxify nitroaromatic pollutants, this study introduces a novel approach for synthesizing cobalt oxide nanocomposites via pyrolysis of cobalt benzene-1,3,5-tricarboxylate. By integrating porous carbon (PC) and nano silica (NS) supports with Co₃O₄ to form (Co₃O₄/PC) and (Co₃O₄/NS), we achieved precise morphological control, as evidenced by SEM and TEM analysis. SEM revealed 80–500 nm Co₃O₄ microspheres, 300 nm Co₃O₄/PC microfibers, and 2–5 µm Co₃O₄/NS spheres composed of 100 nm nanospheres. TEM further confirmed the presence of ~15 nm nanoparticles. Additionally, FTIR spectra exhibited characteristic Co–O bands at 550 and 650 cm⁻¹, while UV–Vis absorption bands appeared in the range of 450–550 nm, confirming the formation of cobalt oxide structures. Catalytic assays toward p-nitrophenol reduction revealed exceptional kinetics (k = 0.459, 0.405, and 0.384 min⁻¹) and high turnover numbers (TON = 5.1, 6.7, and 6.3 mg 4-NP reduced per mg of catalyst), outperforming most of the recently reported systems. Notably, both supported catalysts retained over 95% activity after two regeneration cycles. These findings not only fill a gap in the development of efficient, regenerable cobalt-based catalysts, but also pave the way for practical applications in environmental remediation. Full article

To mitigate the consumption of active sites on co-catalysts by H₂O₂ and to enhance the efficiency and stability of co-catalytic Fenton reactions, an external circulation two-stage packed-bed reactor (ECTPBR) was developed using DPW (diatomite plate@polydopamine@WC) as a co-catalyst to degrade 4-nitrophenol (4-NP). Under suitable conditions, the ECTPBR could achieve over 91.97% 4-NP degradation, with low iron sludge production (11.97 mg/L) and minimal tungsten leaching (3.6363 mg/L). The two-stage strategy enabled spatial separation of Fe³⁺ reduction and Fenton reactions, minimizing the loss of active sites on DPW, ensuring long-term system stability, and reducing the toxicity of 4-NPdegradation products. In addition, external circulation enhanced mass transfer and improved resistance to shock loads. These advantages suggest that the ECTPBR may serve as an effective strategy for applying co-catalytic Fenton reactions in the treatment of toxic and refractory organic wastewater. Full article

Dry Turkish oak (Quercus cerris) sawdust, untreated and treated with three activators, (H₃PO₄, NaOH and H₂O₂) was pyrolyzed under limited-oxygen conditions to obtain biochar samples. The electrochemical properties of these samples were tested and compared to the properties of several commercial carbon blacks. The electrochemical characterization was performed via cyclic voltammetry, analyzing the response toward two commonly used redox probes, [Fe(CN)₆]^3−/−4− and [Ru(NH₃)₆]^2+/3+. The influence of the scan rate on this response was investigated, and the resulting data were used to obtain the values of the heterogenous charge transfer constant, k₀. Higher k₀ values were observed for carbon blacks than for investigated biochar samples. The detection of 4-nitrophenol and heavy metal ions was used to assess the applicability of biochars for electroanalytical purposes. The response of untreated biochar was comparable with the response of Vulcan carbon black, which showed the best response of all analyzed carbon blacks. Full article

An anion exchange-assisted technique was used for the synthesis of platinum-decorated SnO₂ supports, providing nanocatalysts with enhanced activity for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). In this study, a series of SnO₂ supports, namely SnA (synthesized almost at room temperature), SnB (hydrothermally treated at 180 °C), and SnC (annealed at 600 °C), are systematically investigated, all loaded with 1 mol% Pt from H₂PtCl₆ under identical mild conditions. The chloride ions from the SnCl₄ precursors were efficiently removed via a strong-base anion exchange reaction, resulting in highly dispersed, crystalline ~5 nm cassiterite SnO₂ particles. All Pt/SnO₂ composites displayed mesoporous structures with type IVa isotherms and H₂-type hysteresis, with SP1a (Pt on SnA) exhibiting the largest surface area (122.6 m²/g) and the smallest pores (~3.5 nm). STEM-HAADF imaging revealed well-dispersed PtOx domains (~0.85 nm), while XPS confirmed the dominant Pt⁴⁺ and Pt²⁺ species, with ~25% Pt⁰ likely resulting from photoreduction and/or interactions with Sn–OH surface groups. Raman spectroscopy revealed three new bands (260–360 cm⁻¹) that were clearly visible in the sample with 10 mol% Pt and were due to the vibrational modes of the PtOx species and Pt-Cl bonds introduced due the addition and hydrolysis of H₂PtCl₆ precursor. TGA/DSC analysis revealed the highest mass loss for SP1a (~7.3%), confirming the strong hydration of the PtOx domains. Despite the predominance of oxidized PtOx species, SP1a exhibited the highest catalytic activity (k_app = 1.27 × 10⁻² s⁻¹) and retained 84.5% activity for the reduction of 4-NP to 4-AP after 10 cycles. This chloride-free low-temperature synthesis route offers a promising and generalizable strategy for the preparation of noble metal-based nanocatalysts on oxide supports with high catalytic activity and reusability. Full article

Nitrophenols are persistent organic pollutants that pose serious environmental and health risks due to their toxic and lipophilic nature. Their persistence arises from strong aromatic stability and resistance to biodegradation, while their lipophilicity facilitates bioaccumulation, exacerbating ecological and human health concerns. To address this challenge, this study focuses on the synthesis and characterization of two different types of hybrid multi-core magnetic catalysts: (i) cobalt ferrite (Co-Fe₂O₄), which exhibits ferrimagnetic properties, and (ii) magnetite (Fe₃O₄), which demonstrates close superparamagnetic behavior and is coated with a novel and less hazardous phloroglucinol–glyoxal-derived resin. This approach aims to enhance catalytic efficiency while reducing the environmental impact, offering a sustainable solution for the degradation of nitrophenols in aqueous matrices. Transmission electron microscopy (TEM) images revealed the formation of a multi-core shell structure, with carbon layer sizes of 6.6 ± 0.7 nm for cobalt ferrite and 4.2 ± 0.2 nm for magnetite. The catalysts were designed to enhance the stability and performance in catalytic wet peroxide oxidation (CWPO) processes using sol–gel and solution combustion synthesis methods, respectively. In experiments of single-component degradation, the carbon-coated cobalt ferrite (CoFe@C) catalyst achieved 90% removal of 2-nitrophenol (2-NP) and 96% of 4-nitrophenol (4-NP), while carbon-coated magnetite (Fe₃O₄@C) demonstrated similar efficiency, with 86% removal of 2-NP and 94% of 4-NP. In the multi-component system, CoFe@C exhibited the highest catalytic activity, reaching 96% removal of 2-NP, 99% of 4-NP, and 91% decomposition of H₂O₂. No leaching of iron was detected in the coated catalysts, whereas the uncoated materials exhibited similar and significant leaching (CoFe: 5.66 mg/L, Fe₃O₄: 12 mg/L) in the single- and multi-component system. This study underscores the potential of hybrid magnetic catalysts for sustainable environmental remediation, demonstrating a dual-function mechanism that enhances catalytic activity and structural stability. Full article

The use of fibers or fabrics as frameworks for loading photocatalysts is beneficial in solving the problems of photocatalytic nanomaterials, which tend to agglomerate and are difficult to recycle. In this study, Bi₂WO₆/CFb and Bi₂WO₆/Bi₂S₃/CFb photocatalytic fibers rich in oxygen vacancies were prepared using carbon fibers as the framework by the crystal seed attachment method and in situ growth method by using the self-polymerization and strong adhesion properties of dopamine. The results of SEM, TEM and XRD tests showed that Bi₂WO₆ and Bi₂WO₆/Bi₂S₃ nanosheets were uniformly and completely encapsulated on the surface of the carbon fibers. The results of XPS and EPR tests showed that Bi₂WO₆ nanosheets were rich in oxygen vacancies. The PL, transient photocurrent responses and EIS results showed that the introduction of Bi₂S₃ significantly improved the migration efficiency of the photogenerated carriers of Bi₂WO₆/Bi₂S₃/CFb, which effectively hindered the recombination of photogenerated electron–hole pairs. By conducting degradation experiments on p-nitrophenol and analyzing the bandgap structure, it was postulated that the heterojunction structure of Bi₂WO₆/Bi₂S₃/CFb in the Bi₂WO₆/Bi₂S₃ material was not Type-II but Z-scheme. As analyzed by the active species assay, the active species that played a major role in the degradation process were O₂⁻ and h⁺. The incorporation of a small amount of Bi₂S₃ resulted in enhanced photocatalytic degradation activity of Bi₂WO₆/Bi₂S₃/CFb toward tetracycline hydrochloride compared to Bi₂WO₆/CFb. The excellent photocatalytic performance of Bi₂WO₆/Bi₂S₃/CFb photocatalytic fibers can be attributed to the rapid transmission and separation performance and the high oxidation and reduction capacities of photogenerated electron–hole pairs formed by direct Z-scheme heterojunctions. Full article

The availability of water-soluble nanoparticles allows catalytic reactions to occur in highly desirable green environments. The catalytic activity and selectivity of water-soluble palladium nanoparticles capped with 6-(carboxylate)hexanethiolate (C6-PdNP) and 5-(trimethylammonio)pentanethiolate (C5-PdNP) were investigated for the reduction of 4-nitrophenol, the oxidation of α,β-conjugated aldehydes, and the C-C coupling of phenylboronic acid. The study showed that between the two PdNPs, C6-PdNP exhibits better catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride and the selective oxidation of conjugated aldehydes to conjugated carboxylic acids. For the latter reaction, molecular hydrogen (H₂) and H₂O act as oxidants for the surface palladium atoms on PdNPs and conjugated aldehyde substrates, respectively. The results indicated that the competing addition activities of Pd-H and H₂O toward the π-bond of different unsaturated substrates promote either reduction or oxidation reactions under mild conditions in organic solvent-free environments. In comparison, C5-PdNP exhibited higher catalytic activity for the C-C coupling of phenylboronic acid. Gas chromatography–mass spectrometry (GC-MS) was mainly used as an analytical technique to examine the products of catalytic reactions. Full article

Granular activated carbon (GAC) serves as a cost-efficient electrocatalyst cathode in electrochemical water treatment. This study investigates the impact of current intensity and cathode mesh size on the electrocatalytic generation of reactive oxygen species (ROS), i.e., hydrogen peroxide (H₂O₂) and hydroxyl radicals (•OH), for removing p-nitrophenol (PNP) as a representative contaminant. The findings suggest that these parameters exert a factorial effect on PNP removal, which is statistically endorsed via the analysis of variance. The −20 + 40 mesh GAC exhibited superior electrocatalytic performance due to its optimal balance of porosity and active surface area. Additionally, the reactor configuration was also studied. Employing two reactors in series configuration resulted in a 23% increase in H₂O₂ generation and a 32% enhancement in overall PNP removal compared with the single reactor configuration. This enhancement is attributed to (i) the enhanced electroactive area, (ii) the greater retention time of PNP over the electrocatalyst surface, and (iii) the increased dissolved oxygen and H₂O₂ content in the second reactor, promoting the overall H₂O₂ generation. Numerical simulations were conducted to compute H₂O₂ concentration profiles, providing a detailed representation of the physical, chemical, and electrochemical processes. The model exhibited a high degree of accuracy compared with the experimental measurements, with R² values ranging from ~0.76 to 0.99 and MAE values between ~0.04 and 0.23 mg/L. The simulation results highlight a strong interplay between H₂O₂ generation, its reaction kinetics during PNP removal, and electrode utilization efficiency. These findings emphasize the importance of optimizing the applied current magnitude and reactor operation duration to maximize electrode efficiency and H₂O₂ generation and utilization, while minimizing electrochemical bubble blockage. Overall, this study provides fundamental insights to optimize the electroactive area for enhanced ROS generation toward efficient contaminant removal, supporting sustainable groundwater remediation technologies in the face of emerging pollutants. Full article