Design of One-Dimensional Cadmium Sulfide/Polydopamine Heteronanotube Photocatalysts for Ultrafast Degradation of Antibiotics

Critical parameters influencing the continuous performance of upflow microbubble airlift photocatalytic process treating pharmaceutical pollutants

The advances in heterogeneous photocatalysts are still confined to evaluating the functional photocatalytic activity of catalysts in simple batch-mode operation. Nevertheless, the long-term stability, recovery-reusability, and cost-effectiveness of photocatalysts are critical issues in practical applications for pollution control. This study examined the critical parameters to improve the photocatalytic degradation activity of the antibiotic tetracycline and strategized successful continuous performance in a two-stage photocatalytic process adopting sequencing batch-mode microbubble upflow airlift reactor (UALR) followed by the centrifugal separation of CdS nanoparticles (NPs). The most effective strategy for NPs separation was a sequential combination of gravity separation (10 min settling) in the settling phase and subsequent high-speed centrifugation (5 min at 25,000×g) of the settled NPs sediments, providing an economic benefit by reducing the centrifugation capacity. During steady state operation under the optimal conditions, the UALR showed reliable performance, resulting in 97-91% and 85-81% degradation efficiency at 60- and 30-min reaction time per cycle, respectively. A weak basic condition (pH 8) and dissolved oxygen (DO) supplementation increased the photocatalytic activity by 12% (0.0292 min^-1) and 30% (0.0363 min^-1) compared to the control. Trapping studies confirmed the enhanced performance using various reactive oxygen species scavengers, revealing an increase in ^•OH generation (6.5%).

Co-catalyst and heterojunction dual strategies to induce photogenerated charge separation for efficient hydrogen evolution of CdS

The construction of heterojunctions is considered to be an important means to promote efficient electron-hole separation in photocatalysts. However, photocatalysts have poor light absorption ability and a relatively small chance of capturing H⁺, and the stability needs to be improved. In this work, a non-precious metal co-catalyst Cu₃P was introduced for the successful construction of p-n heterojunctions from NiO and CdS to promote charge separation while expanding the light absorption capacity and increasing the chance of H⁺ capture, thus enhancing the photocatalytic hydrogen precipitation activity and stability. The overall photocatalytic performance was improved by continuously optimizing the loading of NiO and Cu₃P. Satisfyingly, using a 5 W LED lamp as the light source, the hydrogen evolution rate of the composite photocatalyst 15NC@Cu-10 in 10 vol% lactic acid solution is 15 612.0 μmol h^-1 g^-1, and the AQE reaches 10.4%. XPS analysis confirmed the direction and path of electron transfer. This synergistic strategy of co-catalyst modification of p-n heterojunctions provides a unique insight into the preparation of efficient and stable photocatalysts and also expands the applications of MOFs and their derivatives in the field of photocatalysis.

Preparation of P-doped CdS nanorods as an efficient photocatalyst for the degradation of the emerging pollutant tetracycline antibiotic under blue LED light irradiation

Excessive drug usage and sewage discharges containing antibiotics have caused water contamination due to the rapid growth of pharmaceutical industries. Tetracycline (TC) is one of the most frequently applied antibiotics having a significant impact on the aquatic environment, water quality and human health and thus effective approaches for TC removal from water are urgently needed. Here, we have fabricated P-doped CdS (CdS-P_0.8) nanorods (NRs) by one-step thermal phosphorization treatment for TC degradation through photocatalytic reaction in the presence of blue and white LED light irradiation. Synthesized photocatalysts were characterized to authenticate the incorporation of P atoms on the CdS NR surface using XPS, XRD, ICP-OES and EDX mapping analyses. CdS-P_0.8 NRs have greater photocatalytic activity for tetracycline degradation under blue LED light irradiation. TC degradation on CdS-P_0.8 NRs followed pseudo-first order kinetics for both LED light sources. In the presence of blue LED light at an intensity of 10 mW cm^-2, TC degradation efficiency and pseudo-first order rate constants of CdS-P_0.8 NRs for the photocatalytic degradation reaction reached 95.4% and 0.13396 min^-1 in 20 minutes without any supplemental oxygen sources. Scavenging experiments demonstrate that reactive oxygen species are produced during the photocatalytic degradation of tetracycline. As a result, due to the extensive utilization of photogenerated oxidative species such as h⁺, O₂˙^- and OH˙, CdS-P_0.8 NRs demonstrated high photocatalytic tetracycline degradation efficiency in 20 minutes. Our findings shed more light on nonmetal P doping on CdS materials and other semiconductors, exploring new possibilities for photocatalytic degradation to efficiently reduce the amount and toxicity of TC antibiotics in wastewater.