Visible light-driven NH2Cl activation by g-C3N4 photocatalysis producing reactive nitrogen species to degrade bisphenol A

Insights into copper(I) phenylacetylide with in-situ transformation of oxygen and enhanced visible-light response for water decontamination: Cu-O bond promotes exciton dissociation and charge transfer

The widespread contamination of hexavalent chromium (Cr(VI)), pharmaceuticals and personal care products (PPCPs), and dyes is a growing concern. necessitating the development of convenient and effective technologies for their removal. Copper(I) phenylacetylide (PhC2Cu) has emerged as a promising photocatalyst for environmental remediation. In this study, we introduced a functional Cu-O bond into PhC2Cu (referred to as OrPhC2Cu) by creatively converting the adsorbed oxygen on the surface of PhC2Cu into a Cu-O bond to enhance the efficiency of Cr(VI) photoreduction, PPCPs photodegradation, and dyes photodegradation through a facile vacuum activating method. The incorporation of the Cu-O bond optimized the electron structure of OrPhC2Cu, facilitating exciton dissociation and charge transfer. The exciton dissociation behavior and charge transfer mechanism were systematically investigated for the first time in the OrPhC2Cu system by photoelectrochemical tests, fluorescence and phosphorescence (PH) techniques, and density functional theory (DFT) calculations. Remarkably, the enhanced visible-light response of OrPhC2Cu improved photon utilization and significantly promoted the generation of reactive species (RSs), leading to the highly efficient Cr(VI) photoreduction (98.52% within 25 min) and sulfamethazine photodegradation (94.65% within 60 min), with 3.91 and 5.23 times higher activity compared to PhC2Cu. Additionally, the photocatalytic efficiency of OrPhC2Cu in degrading anionic dyes surpassed that of cationic dyes. The performance of the OrPhC2Cu system in treating electroplating effluent or natural water bodies suggests its potential for practical applications.

Novel sunlight-induced monochloramine activation system for efficient microcontaminant abatement

As an eco-friendly and sustainable energy, solar energy has great application potential in water treatment. Herein, simulated sunlight was for the first time utilized to activate monochloramine for the degradation of environmental organic microcontaminants. Various microcontaminants could be efficiently degraded in the simulated sunlight/monochloramine system. The average innate quantum yield of monochloramine over the wavelength range of simulated sunlight was determined to be 0.068 mol/Einstein. With the determined quantum yield, a kinetic model was established. Based on the good agreement between the simulated and measured photolysis and radical contributions to the degradation of ibuprofen and carbamazepine, the major mechanism of monochloramine activation by simulated sunlight was proposed. Chlorine radical (Cl∙) and hydroxyl radical (HO∙) were major radicals responsible for microcontaminant degradation in the system. Moreover, the model facilitated a deep investigation into the effects of different reaction conditions (pH, monochloramine concentration, and water matrix components) on the degradation of ibuprofen and carbamazepine, as well as the roles of the involved radicals. The differences between simulated and measured degradation data of each microcontaminant under all conditions were less than 10 %, indicating the strong reliability of the model. The model could also make good prediction for microcontaminant degradation in the natural sunlight/monochloramine system. Furthermore, the formation of disinfection byproducts (DBPs) was evaluated at different oxidation time in simulated sunlight/monochloramine with and without post-chloramination treatment. In real waters, organic components showed more pronounced suppression on microcontaminant degradation efficiency than inorganic ions. This study provided a systematic investigation into the novel sunlight-induced monochloramine activation system for efficient microcontaminant degradation, and demonstrated the potential of the system in practical applications.

Photochemical Transformation of Monochloramine Induced by Triplet State Dissolved Organic Matter

The photoexcited dissolved organic matter (DOM) could produce reactive intermediates, affecting chemical oxidant transformation in UV based advanced oxidation processes (AOPs). This study confirmed the critical role of triplet state DOM (3DOM*), generated from DOM photoexcitation, in the transformation of monochloramine (NH2Cl), a commonly used chemical oxidant and disinfectant in water treatment. NH2Cl (42.25 μM, as Cl2) was decayed by 17.4-73.4 % within 60 min, primarily due to 3DOM* , in DOM (2-30 mgC L-1) solutions irradiated by 365 nm, where NH2Cl has no absorption. The second-order quenching rate constants of triplet state model photosensitizers by NH2Cl were determined to be 0.95(± 0.04)-4.49(± 0.04)× 108 M-1 s-1 by using laser flash photolysis. As a reductant, 3DOM* reacted with NH2Cl through one-transfer mechanism, leading to amino radical (NH2•) generation, which then transferred to ammonia (NH4+, pKa 9.25) through H-abstraction by the phenolic moieties in DOM. Additionally, the intermediate product of 3DOM* oxidized by NH2Cl or those triplet state quinones can hydrolyze to form phenolic moieties, elevating NH4+ yield to higher than 99% upon 365 nm irradiation. These findings suggest that the widespread DOM can be applied to convert NH2Cl via 3DOM* with minimal toxic risks.

Dissolved Organic Matter-Mediated Photosensitized Activation of Monochloramine for Micropollutant Abatement in Wastewater Effluent

Utilizing solar light and water matrix components in situ to reduce the chemical and energy demands would make treatment technologies more sustainable for micropollutant abatement in wastewater effluents. We herein propose a new strategy for micropollutant abatement through dissolved organic matter (DOM)-mediated photosensitized activation of monochloramine (NH2Cl). Exposing the chlorinated wastewater effluent with residual NH2Cl to solar irradiation (solar/DOM/NH2Cl process) degrades six structurally diverse micropollutants at rate constants 1.26-34.2 times of those by the solar photolysis of the dechlorinated effluent (solar/DOM process). Notably, among the six micropollutants, the degradation rate constants of estradiol, acetaminophen, bisphenol A, and atenolol by the solar/DOM/NH2Cl process are 1.13-4.32 times the summation of those by the solar/DOM and solar/NH2Cl processes. The synergism in micropollutant degradation is attributed to the generation of reactive nitrogen species (RNS) and hydroxyl radicals (HO·) from the photosensitized activation of NH2Cl. Triplet state-excited DOM (3DOM*) dominates the activation of NH2Cl, leading to the generation of RNS, while HO· is produced from the interactions between RNS and other photochemically produced reactive intermediates (e.g., O2·- and DOM·+/·-). The findings advance the knowledge of DOM-mediated photosensitization and offer a sustainable method for micropollutant abatement in wastewater effluents containing residual NH2Cl.

Green synthesis of ZnO nanocubes from Ceropegia omissa H. Huber extract for photocatalytic degradation of bisphenol An under visible light to mitigate water pollution

Plastic pollution has become a major environmental problem because it does not break down and poses risks to ecosystems and human health. This study focuses on the environmentally friendly synthesis of ZnO nanocubes using an extract from Ceropegia omissa H. Huber plant leaves. The primary goal is to investigate the viability of these nanocubes as visible-light photocatalysts for the degradation of bisphenol A (BPA). The synthesized ZnO nanocubes have a highly crystalline structure and a bandgap of 3.1 eV, making them suitable for effective visible-light photocatalysis. FTIR analysis, which demonstrates that the pertinent functional groups are present, demonstrates the chemical bonding and reducing processes that take place in the plant extract. The XPS method also studies zinc metals, oxygen valencies, and binding energies. Under visible light irradiation, ZnO nanocubes degrade BPA by 86% in 30 min. This plant-extract-based green synthesis method provides a long-term replacement for traditional procedures, and visible light photocatalysis has advantages over ultraviolet light. The study's results show that ZnO nanocubes may be good for the environment and can work well as visible light photocatalysts to break down organic pollutants. This adds to what is known about using nanoparticles to clean up the environment. As a result, this study highlights the potential of using environmentally friendly ZnO nanocubes as a long-lasting and efficient method of reducing organic pollutant contamination in aquatic environments.

In Situ Fabrication of a 2D/2D MXene/CN Heterojunction for Photothermally Assisted Photocatalytic Sterilization under Visible Light Irradiation

Constructing an efficient visible light-responsive antibacterial material for water treatment remains a principal goal yet is a huge challenge. Herein, a 2D/2D heterojunction composite with robust interfacial contact, named MXene/CN (MCN), was controllably fabricated by using a urea molecule intercalated into MXene following an in situ calcination method, which can realize the rapid separation and migration of photogenerated carriers under visible light irradiation and significantly improve the carrier concentration of the MXene surface, thus generating more reactive oxygen species. The generation of heat induced by MXene could also increase photogenic electron activity to facilitate the photocatalytic reaction using in situ time-resolved photoluminescence characterization. The visible light-activated germicide exhibits a sterilization efficacy against Escherichia coli of 99.70%, higher than those of pure CN (60.21%) and MXene (31.75%), due to the effect of photothermally assisted photocatalytic treatment. This work is an attempt to construct a visible light-driven antimicrobial material using Schottky junctions achieving photothermally assisted photocatalytic disinfection.

Reevaluation for UV photolysis of Fe(III) inducing tetracycline abatement: Overlooked significance of complexation-assistance in environmental fates of antibiotics

Interaction of antibiotics with metal ions in aquatic environments, commonly occurring to form complexes, may affect the migration, transformation and reactivity of residual antibiotics. This study demonstrates the photolysis of Fe(III) by UV irradiation at pH 3.5, as an advanced oxidation process, to produce •OH for the abatement of a common broad-spectrum antibiotic compound, tetracycline (TET). The dimethylamino (-N(CH₃)₂) and hydroxyl (-OH) groups of TET were determined as the binding sites for the complexation with Fe(III) via a series of novel characterization approaches. The complexation stoichiometry of Fe(III)-TET complexation, including the complexation ratio, constants and percentages, was determined via a complexometric titration based on the UV differential spectroscopy. The complexation constant was determined to be 21,240 ± 1745 L·mol^-1 under the designed conditions. Complexation of TET with Fe(III) enhanced its degradation in the UV/Fe(III) process, through the promotion of the •OH generation by inhibiting hydrolysis-precipitation process of Fe(III) and enhancing Fe(III)/Fe(II) cycle and the acceleration of mass transfer between •OH and TET. This finding provides new insights into the role of complexation in the fate of residual antibiotics in the UV/Fe(III) process. The reduced overall ecotoxicity during the TET abatement, evaluated by the toxicity variation through ECOSAR program, provides the UV/Fe(III) process with a theoretical feasibility for water decontamination in actual applications.

Novel polymer optical fibers with high mass-loading g-C3N4 embedded metamaterial porous structures achieve rapid micropollutant degradation in water

The performance of conventional photocatalytic reactors suffers from low photocatalyst mass-loading densities affixed to surfaces and light scattering losses or light attenuation in slurry reactors. These limitations are overcome by fabrication of high mass-loading g-C3N4 embedded metamaterial porous structures on flexible polymeric optical fibers (g-C3N4-POFs). In this study, the fabricated g-C3N4-POFs contain g-C3N4 with mass-loading 100-1000x higher than previouly reported, enabling efficient light delivery to g-C3N4 and improved pollutant mass transport within metamaterial porous structures. The key fabrication step involved using acetone, based on its high saturated vapor pressure and low dielectric constant, making roll-to-roll mass production of high mass-loading photocatalyst-embedded metamaterial POFs possible at room-temperature within seconds. Using bundles of 150 individual g-C3N4-POFs in the reactors, we achieved 4x higher degradation rates for micropollutants under visible light irradiation at 420 nm compared with equivalent mass-to-volume ratios of photocatalysts in a slurry suspension reactor. The bundled g-C3N4-POF reactor showed no degradation in the structural integrity or loss of pollutant degradation using deionized or model drinking water under accumulated HO• exposures of ∼4.5 × 10-9 M•s after 20 cycles of treatment. It operates continuously at g-C3N4 dosages equivalent to 100-1000 g/L and a water depth over 40 cm, making it a feasible alternative to conventional photocatalytic reactors.