Tin(IV) oxide (SnO2) was deposited onto acid-washed multiwalled carbon nanotubes (MWCNTs) to be used as a support for platinum nanoparticles (PtNPs). The effect of the SnO2–CNT support on the electrocatalytic activity of the PtNPs for the oxygen reduction reaction (ORR) in 0.1 M HClO4 solution was investigated. The physical characterization of the catalyst confirms the presence of Pt, Sn and C on the catalyst as well as the presence of the PtNPs on SnO2. The synthesized catalyst possesses a specific activity of 0.15 mA cm−2 at 0.9 V, while the commercial Pt/C catalyst showed a specific activity of 0.05 mA cm−2. Accelerated durability testing (ADT) was performed on both catalysts, with the synthesized PtNP/SnO2–CNT catalyst retaining over 50% of its initial electrochemically active surface area (ECSA). Thus, the results obtained in this study confirm the positive influence of SnO2-decorated CNTs on the overall electrocatalytic activity of PtNPs and their stability toward the ORR.

Phytoremediation is considered as a green alternative for remediating metal-contaminated soil and water, yet further efforts are needed to minimise secondary pollution after phytoremediation. This study investigates a cost-effective and sustainable method to synthesise carbon quantum dot supported on zinc oxide (CQD-ZnO) composites using extracted zinc (Zn) from post-phytoremediated plants, plant extracts, and CQDs derived from water hyacinth (Eichhornia crassipes) for the sonocatalytic degradation of malachite green. The CQD-ZnO materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) surface analysis, and ultraviolet–visible (UV–Vis) spectroscopy to confirm their crystalline structure, morphology, functional groups, surface area, and optical properties. The composites exhibited disaggregation of agglomerates, high crystallinity, and increased carbon content due to the addition of CQDs containing phenolic functional groups (e.g., polyphenols, flavonoids) from the plant extract. The highest sonocatalytic degradation efficiency (84.52%) was achieved after 90 min of treating 10 ppm malachite green using 1 g/L of the CQD-ZnO composite at a natural pH, with 300 W ultrasonic power at 25 kHz. This study paves the way for the development of environmentally friendly, high-performance sonocatalysts from post-phytoremediated plants for wastewater treatment applications.

Selective oxidation of benzyl alcohol to benzaldehyde is crucial for sustainable chemical synthesis, which provides the atom-economical and environmentally benign pathways. In this work, we used the in situ reduction immobilization to synthesize a series of Au nanoparticles supported by CoAlOx support with spinel structure for alkali-free oxidation of benzyl alcohol. The synthesis methodology was preliminarily optimized and the influence of Co/Al molar ratio in Au/CoAlOx on the catalytic performances was subsequently revealed based on characterizations. Results suggested that the electronic interaction between Au and CoAlOx can be regulated and maximized under the Co/Al ratio of 3. It became a main factor to modulate the dispersion of Au nanoparticles, surface chemical composition, as well as the oxygen adsorption/activation ability. Benefiting from such synergistic interaction, the optimized Au/Co3AlOx catalyst achieved 86.1% BnOH conversion under 99.9% benzaldehyde selectivity with well-maintained structural stability under recycle tests. This work provides a rational design strategy for developing highly efficient gold catalysts with well-constructed Au-support interfaces for the alkali-free oxidation of alcohol.

The ability of ultrasound/peracetic acid (US/PAA) to degrade the azo dye Sunset Yellow FCF (SSY) was evaluated considering the impacts of power, pH, inorganic carbon, common salts, radical scavengers, and real water matrices. Pseudo-first-order rate constants revealed synergy indices of 2.90, 3.28, 2.22, and 2.03 at electrical powers of 40, 60, 80, and 100 W, respectively. Selective scavenger assays revealed a mixed radical regime. •OH radical involvement was confirmed by inhibition with alcohols (tert-butanol, 2-propanol), benzoic acid, nitrobenzene, sodium azide, and phenol, while suppression by TEMPO highlighted the key role of PAA-derived acyl and peroxyl radicals. Nitrobenzene caused pronounced inhibition at elevated doses, while nitrite acted as a decisive quencher by converting •OH and other oxidants into less reactive species. Carbonate alkalinity exerted dual effects: at acidic pH (3.7–4.4) it diverted •OH radicals to carbonate radicals and reduced cavitation through dissolved CO2, whereas at near-neutral pH it buffered conditions toward the optimum (pH 9) and enhanced degradation. Common anions (chloride, sulfate, nitrate) at ≤10 mM produced minor effects. Tests in environmental waters revealed the following reactivity order: seawater > ultrapure water > tap water ≈ Zamzam water > tertiary effluent. Enhanced performance in seawater was attributed to halide-mediated formation of reactive chlorine and bromine species, while inhibition in effluent was linked to organic matter scavenging. Overall, US/PAA emerges as a robust and adaptable advanced oxidation process for azo dye abatement across diverse water matrices.

This study transformed discarded courgette biomass into biochar (BC) via pyrolysis at 500 °C and employed it as an activator of potassium periodate (PI) for atrazine (ATZ) degradation. Characterization analyses confirmed that the synthesized BC possessed a porous structure, a high carbon content (76.13%), crystalline SiO2, KCl, and CaCO3 phases, as well as abundant oxygen-containing functional groups (–OH, C=O, C=C, –COOH), which are favorable for catalytic activation. The point of zero charge of 4.25 indicates that the BC surface carries a suitable charge distribution, promoting effective electrostatic interactions under near-neutral pH conditions. Under optimal operating conditions (neutral pH, [ATZ]o = 7.3 mg/L, [PI]o = 2.7 mM, [BC]o = 0.55 g/L, and 25 ± 0.5 °C), the system achieved 99.35% ATZ removal (first-order kinetic rate constant = 0.0601 min−1) and 64.23% TOC mineralization within 60 min. Quenching tests confirmed iodate radicals and singlet oxygen as the primary species, with hydroxyl and superoxide radicals playing secondary roles. The proposed mechanism suggests that electron transfer from oxygen-containing groups on the BC surface activates PI, leading to the generation of reactive oxygen species that facilitate ATZ degradation via synergistic radical and non-radical pathways. The BC catalyst exhibited strong recyclability, with only ~9% efficiency loss after five cycles. The BC/PI system also demonstrated high removal of tetracycline (79.54%) and bisphenol A (85.6%) within 60 min and complete Congo red dye degradation in just 30 min. Application to real industrial wastewater achieved 72.77% ATZ removal, 53.02% mineralization, and a treatment cost of 1.2173 $/m3, demonstrating the practicality and scalability of the BC/PI system for sustainable advanced wastewater treatment.

Hydrogen peroxide (H2O2) is a vital chemical with extensive applications in industries such as agriculture, pharmaceuticals, textiles, water treatment, and food preservation. However, traditional production methods, particularly the anthraquinone process, are energy-intensive, environmentally detrimental, and economically challenging. This review explores the emerging role of covalent organic frameworks (COFs) as sustainable and efficient catalysts for environmentally sustainable generation of H2O2 through photocatalytic and electrocatalytic pathways. COFs, with their tunable porosity, high surface area, and functionalization capabilities, offer unique advantages in enhancing catalytic performance, including improved mass transport, optimized charge transfer, and stabilization of reaction intermediates. Recent advancements in COF-based systems have demonstrated significant improvements in H2O2 yields, driven by innovative designs such as hierarchical pore structures, functional group incorporation, and hybrid composites with conductive materials. Additionally, the integration of COFs into flexible electrode architectures and on-site detection technologies highlights their potential for scalable and practical applications. Despite these advancements, challenges related to catalytic stability, scalability, and industrial integration remain. This review provides a comprehensive overview of the mechanisms, design principles, and performance of COF-based H2O2 generation systems, while identifying future research directions to address existing limitations. By leveraging the unique properties of engineered COFs, this work underscores their transformative potential in advancing sustainable H2O2 production, paving the way for greener and more efficient industrial processes.

Nitrogen oxides (NOx) are major atmospheric pollutants, and their escalating emissions, driven by rapid economic development and urbanization, pose a severe threat to both the ecological environment and human health. Conventional denitrification technologies are often hampered by high costs, significant energy consumption, and stringent operational conditions, making them increasingly inadequate in the face of tightening environmental regulations. In this context, photocatalytic technology, particularly systems based on graphitic carbon nitride (g-C3N4), has garnered significant research interest for NOx removal due to its visible-light responsiveness, high stability, and environmental benignity. To advance the performance of g-C3N4, numerous modification strategies have been explored, including morphology control, elemental doping, defect engineering, and heterostructure construction. These approaches effectively broaden the light absorption range, enhance the separation efficiency of photogenerated electron-hole pairs, and improve the adsorption and conversion capacities for NOx. Notably, constructing heterojunctions between g-C3N4 and other materials (e.g., metal oxides, noble metals, metal–organic frameworks (MOFs)) has proven highly effective in boosting catalytic activity and stability. Furthermore, the underlying photocatalytic mechanisms, encompassing the generation and migration pathways of charge carriers, the redox reaction pathways of NOx, and the influence of external factors like light intensity and reaction temperature, have been extensively investigated. From an application perspective, g-C3N4-based photocatalysis demonstrates considerable potential in flue gas denitrification, vehicle exhaust purification, and air purification. Despite these advancements, several challenges remain, such as limited solar energy utilization, rapid charge carrier recombination, and insufficient long-term stability, which hinder large-scale implementation. Future research should focus on further optimizing the material structure, developing greener synthesis routes, enhancing catalyst stability and poison resistance, and advancing cost-effective engineering applications to facilitate the practical deployment of g-C3N4-based photocatalytic technology in air pollution control.

Enhancing the oxidation resistance of copper nanoparticles (CuNPs) is a crucial objective in plasmonic photocatalytic reactions. In this study, a series of Cu/X catalysts was synthesized using semiconductor nanomaterials (X = TiO2, ZnO, BN, TiN, SiC, and C3N4) as supports for CuNPs. These catalysts were systematically evaluated in visible-light-driven photocatalytic oxidative homocoupling of phenylacetylene (OHA). Comprehensive characterization revealed distinct metal-support interactions and nanostructure evolution during repeated catalytic cycles. The photocatalytic performance, copper leaching, and structural stability of the catalysts were compared. Cu/TiO2 achieved the highest 1,3-diyne yield (up to 93%) in the first two cycles. In contrast, Cu/ZnO showed minimal copper leaching and excellent recyclability, retaining high activity over three consecutive cycles without the need for reduction pretreatment. Comparative studies revealed that the combination of localized surface plasmon resonance (LSPR) and efficient electron transfer within the Cu0-Cu2O-CuO composite was a key factor in enhancing the photocatalytic activity and stability. These findings provide new insights into the rational design of durable CuNP-based photocatalysts for visible-light-driven organic transformations.

Micro-nano bubbles (MNBs) have been widely used in water treatment due to their large specific surface area, long retention time, and high zeta potential. This study investigated the degradation of bisphenols by activating persulfate (PDS, an oxidizing agent) with air MNBs (MNBs/PDS). The removal rate of bisphenol A (BPA) in the MNBs/PDS process was 98.3% within 25 min, while there was almost no degradation observed by PDS or MNBs alone. This enhancement was attributed to the huge amount of energy released during the collapse of MNBs, sufficient to break the O–H bonds of water molecules or the O–O bond of PDS to induce the formation of reactive oxygen species (ROS, such as HO• and SO4•−). To qualitatively analyze ROS generated in this system, electron paramagnetic resonance and quenching experiments were conducted, and the HO• and SO4•− were detected in MNBs/PDS. Furthermore, the degradation percentages of bisphenols after 25 min of MNBs/PDS treatment followed the order of bisphenol B (100%) > BPA (98.3%) > bisphenol E (87.9%) > bisphenol F (86.5%) > bisphenol AF (84.9%) > bisphenol S (51%). Higher PDS dosage, higher gas flow rate, and lower pH values were preferred for the degradation. Moreover, the MNBs/PDS treatment reduced the TOC of secondary effluent containing BPA by 45.8% in one hour, indicating the application potential of MNBs/PDS in the advanced treatment of wastewater.

In this study, we investigate the electrochemical performance of a carboxyl-functionalized pencil graphite (CFPG) electrode for chloride ion oxidation and its subsequent application in dye degradation. The graphite electrode was chemically modified using acetic acid to introduce –COOH functional groups, enhancing surface polarity and chloride adsorption capacity. Surface characterization by SEM, EDX, and XPS confirmed morphological changes and oxygen enrichment following functionalization. Electrochemical measurements demonstrated a positive shift in open circuit potential (OCP) and significantly enhanced chloride oxidation activity, as evidenced by cyclic voltammetry (CV) in 0.1 M KCl. The functionalized electrode facilitated the in situ generation of reactive chlorine species (RCS), with spectral features near ~240 nm consistent with HOCl/ClO− and a broader band around ~450 nm attributable to chlorine-derived intermediates rather than exclusively to molecular chlorine. These species played a central role in degrading structurally diverse dyes—Kenacid Green and Brilliant Green—via oxidative pathways. The results highlight the potential of low-cost, –COOH-modified graphite electrodes as effective platforms for the RCS-mediated electrochemical treatment of organic contaminants.