Photocatalytic degradation of tetracycline using surface defective black TiO2-ZnO heterojunction photocatalyst under visible light

Hybridizing black liquor-derived kraft lignin with Ag3PO4@ZnO to boost tetracycline and dye removal through synergistic adsorption-photocatalytic pathways

Discharging pulping black liquor waste and industrial wastewater, such as that from the pharmaceuticals and textiles, into surface water can poses risks to both human health and aquatic ecosystems. Accordingly, this research introduces an innovative method for valorizing pulping black liquor waste by extracting kraft lignin (KL) as a sustainable biopolymer for constructing a ternary KL-supported Ag3PO4@ZnO p-n heterojunction (designated as AZC-KL(x), with x denotes the wt. % ratios of AZC (Ag3PO4@ZnO): KL at 1: 0.2, 1: 0.5, and 1: 1). The AZC-KL(x) composites are evaluated for the enhanced removal of mixed textile (e.g., methylene blue (MB) and methyl orange (MO) dyes) and pharmaceutical (e.g., tetracycline (TC)) pollutants through synergistic adsorption/photocatalytic mechanisms under dark/visible light conditions, in comparison to the pristine Ag3PO4@ZnO, as well as KL-supported Ag3PO4 or ZnO binary composites. In comparison to the AZC heterojunction, the AZC-KL(x) significantly improves the adsorption rate of three pollutants by a factor of 1.66 - 3.81. This enhancement is attributed to π-π stacking and hydrogen bonding with the oxygen-containing groups and aromatic structure of the KL substrate. In particular, AZC-KL(1) demonstrates superior adsorption-photocatalytic activity, sustaining its effectiveness over five cycles. It exhibits the highest removal rate for MB dye with a kapp of 3.26 × 10-2 min-1 and an apparent quantum yield (AQY) of 16.4 × 10-7 mol/E across 180 min of visible light irradiation, which is 6.4 and 9.5 times higher than that of TC and MO, respectively. Lowering the KL ratio to 1: 0.2 in the AZC-KL(x) structure leads to a performance decline by 1.18 - 2.1 times (relative to AZC-KL(1)), demonstrating the importance of KL in tailoring the surface chemistry and optoelectronic characteristics of AZC-KL(x), as verified by various analytical methods. This collaborative method lowers the energy required for effective wastewater treatment and decreases treatment costs, as demonstrated in the techno-economical analysis.

Ex Situ Fabrication of the G-TiO2 Nanocomposite with Tunable Physiochemical Characteristics for Enhanced Photocatalytic Performance

This study reports fabrication of graphene-titanium dioxide (G-TiO2) nanocomposites with varying graphene content (0%, 25%, 50%, and 75%) through a sonication-assisted co-precipitation method. The synthesized materials were analyzed through FTIR, DRS, SEM, and XRD techniques, which confirmed the successful formation of an anatase-phase TiO2 tetragonal structure with crystallite sizes ranging from 10 to 25 nm after calcination at 600 °C for 4 h. The addition of graphene resulted in a significant reduction in the TiO2 bandgap energy from 3.2 eV to 1.55 eV, enhancing the material's absorption in the visible-light spectrum. The nanocomposite with 50% graphene loading exhibited strong adsorption and the highest photocatalytic efficiency, achieving 98.29% degradation of cationic methylene blue dye under visible-light irradiation. This exceptional performance is attributed to the synergistic effects of graphene, including improved light absorption, enhanced charge carrier separation, and increased electron transfer efficiency. Kinetic analysis revealed that the photocatalytic degradation followed pseudo-first-order reaction kinetics. Furthermore, recycling tests demonstrated the structural stability and reusability (up to 5 cycles) of the nanocomposite, indicating its potential as an effective photocatalyst for environmental applications. The effectiveness of G-TiO2 in mitigating industrial pollutants also underscores the significance of the sonication-assisted co-precipitation approach.

TiO2-ZnO functionalized low-cost ceramic membranes from coal fly ash for the removal of tetracycline from water under visible light

Hybrid wastewater treatment systems offer viable solutions to enhance the removal of complicated contaminants from aqueous system. This innovation has opened new avenues for advanced wastewater treatment processes. Herein, a novel TiO2-ZnO functionalized coal fly ash-based ceramic membrane was fabricated by utilizing a combined pressing and sintering method. The intrinsic properties of the functionalized membranes were characterized and their chemical and physical properties such as chemical stability, mechanical stability, water absorption, and porosity were established. The shape, crystallinity, thermal characteristics, and functional groups present were also determined using SEM, XRD, TGA, and FTIR studies, respectively. The results showed that the ceramic membrane functionalized with 0.5 g of TiO2-ZnO and sintered at 850 °C exhibited the best thermal, and chemical stability, and possessed the required porosity for ultrafiltration applications. Photocatalytic degradation of tetracycline (TC) as a model pollutant was examined and the optimum efficiency of 77% was achieved within 100 min of visible irradiation using the functionalized membrane. Moreso, the functionalized membrane was found to be stable with 73% degradation efficiency after 5 consecutive cycles of reusability study, showing negligible loss of efficiency. The scale-up of photocatalytic ceramic membranes and their utilization in real industrial applications will confirm their robustness.

Construction of oxygen-rich vacancies and heterojunctions coupled with different morphologies of CeO2/mesoporous TiO2 framework structures for efficient photocatalytic CO2 reduction performance

The coupling of efficient adsorption and effective charge separation with photocatalysts enables the use of sunlight for photocatalytic reduction of carbon dioxide (CO2) into high-value-added products. In this work, we used a straightforward solid-phase hydrothermal technique to build an oxygen-vacancy-rich, heterogeneous interface-coupled CeO2/mesoporous TiO2 framework structural system. The heterogeneous structure was constructed by introducing oxygen-vacancy-rich CeO2 into mesoporous TiO2, which may encourage the transfer of charges and increase the number of active sites and CO2 adsorption by utilizing the coupled synergistic effect of oxygen vacancies and heterogeneous interfaces, and it can also regulate the pathway of the photocatalytic reaction and the selectivity of the products. The composite of CeO2 with different morphologies and oxygen-rich vacancies regulated the system's active sites and degree of exposure and enhanced photocatalytic CO2 reduction. The highest CO yield of 6.25 mmol gcat-1 was obtained by use of the rod CeO2/mesoporous TiO2 composite photocatalyst (R-CeO2/TiO2), and this yield was 1.6 times higher than that of pure mesoporous TiO2 and 1.84 times higher than that of pure R-CeO2. Also, the product selectivity increased by 4.3% compared to a single sample. Combining the Mott-Schottky plot results and the energy-barrier perspective to further explore the photocatalytic reduction of the CO2 reaction mechanism as well as the product selectivity, it appears that the construction of the composite system of oxygen-rich vacancies and heterogeneous boundary-coupled photocatalysis provides a practical pathway for the photocatalytic reaction, which may contribute to the photocatalytic reaction's high efficiency and yield selectivity.

Understanding the variations in degradation pathways and generated by-products of antibiotics in modified TiO2 and ZnO photodegradation systems: A comprehensive review

This review examines various modification techniques, including metal doping, non-metal doping, multi doping, mixed doping, and the construction of heterojunction photocatalysts, for enhancing the performance of pure TiO2 and ZnO in the photodegradation of antibiotics. The study finds that mixed and multi doping approaches are more effective in improving photodegradation performance compared to single doping. Furthermore, the selection of suitable semiconductors for constructing heterojunction photocatalysts is crucial for achieving an efficient charge carrier separation. The environmental impacts, recent research, and real application of photocatalysis process have been discussed. The review also investigates the impact of operating parameters on the degradation pathways and the generation of by-products for different antibiotics. Additionally, the toxicity of the by-products resulting from the photodegradation of antibiotics using modified ZnO and TiO2 photocatalysts is explored, revealing that these by-products may exhibit higher toxicity than the original antibiotics. Consequently, to enable the widespread implementation of photodegradation systems, researchers should focus on optimizing degradation systems to control the conversion pathways of by-products, developing innovative photoreactors, and evaluating toxicity in real wastewater matrices.

Application of coal fly ash based ceramic membranes in wastewater treatment: A sustainable alternative to commercial materials

The continued increase in the global population has resulted in increased water demand for domestic, agricultural, and industrial purposes. These activities have led to the generation of high volumes of wastewater, which has an impact on water quality. Consequently, more practical solutions are needed to improve the current wastewater treatment systems. The use of improved ceramic membranes for wastewater treatment holds significant prospects for advancement in water treatment and sanitation. Hence, different studies have employed ceramic membranes in wastewater treatment and the search for low-cost and environmentally friendly starting materials has continued to engender research interests. This review focuses on the application of coal fly ash in membrane technology for wastewater treatment. The processes of membrane fabrication and the various limitations of the material. Several factors that influence the properties and performance of coal fly ash ceramic membranes in wastewater treatment are also presented. Some possible solutions to the limitations are also proposed, while cost analysis of coal fly ash-based membranes is explored to evaluate its potential for large-scale applications.