Self-polarized schorl optimizing TiO2 for photocatalytic persulfate activation and organic pollutants degradation

Construction of a CuO/TiO2@C S-scheme heterojunction for phenol removal by activated peroxymonosulfate

Phenol is a volatile organic compound whose effective degradation using conventional methods is challenging. Rapid charge-carrier recombination and slow Cu(II)/Cu(I) conversion rate in copper-based photocatalysts hinder their activation efficiency of potassium persulfate (PMS). Herein, an S-scheme heterojunction structure comprising TiO2@C and CuO was successfully constructed using an in situ calcination method, enabling the spatial separation of photogenerated charge carriers and thus enhancing the synergistic effect of PMS in the photocatalytic degradation of phenol. The resulting CuO/TiO2@C nanocomposite exhibited notably higher phenol removal efficiency than CuO or TiO2@C alone, removing an 88 % phenol (40 mg/L) and a 48 % total organic carbon within 25 min. The material maintained high degradation efficiency after four cycles. Liquid chromatography-mass spectrometry was employed to identify intermediates generated during phenol degradation, and a potential charge-transfer mechanism was proposed based on the analysis of catalytic active species and energy band structure. Thus, this study provides new insights for enhancing PMS activation for phenol remediation.

Real "zero energy consumption" for efficient antibiotics degradation by floating photocatalysis: modeling, degradation pathway and toxicity assessment

Floating photocatalysis is a real "zero energy consumption" and practicable green water treatment technology because of no need for reactor and pump, and direct contact with sunlight to produce more free radicals compared to traditional immersion photocatalysts. To realize "green" and "safe" practical application, efficiency for different water quality bodies and toxicity assessment of degradation products are key factors. In this work, an economic and efficient floating photocatalyst Bi doped P25-TiO2 (Bi@P25)/expanded perlite (EP), named BTEP was successfully constructed, exhibiting stronger visible light absorption and faster photogenerated carriers separation ability due to Bi doping and formation of Bi-O-Si bond. Ciprofloxacin (CIP) degradation efficiency (10 mg/L) in deionized water and three types of ambient water reached 97.8 % and 52.9 %-75.2 %, respectively, based on the major active species (h+ and •O2-). Three degradation pathways were determined and the reduced toxicity of most intermediates proved the process is green and safe. BTEP had strong adaptability over a wide pH range (3-9). The degradation efficiency is promoted by higher temperatures, while depressed by humic acid (HA) (still maintain over 65.3 % at 15 mg/L of HA). Moreover, the Random Forest model is the most suitable to achieve degradation efficiency prediction of different water parameters duo to the lowest root mean square error (RMSE) value (9.52) and the highest R2 value (0.9045). The BTEP based floating photocatalysis promotes the practical application of solar photocatalytic technology and realizes zero energy consumption to remove pollutants.

TiO2-based photocatalysts from type-II to S-scheme heterojunction and their applications

Photocatalysis is a promising sustainable technology to remove organic pollution and convert solar energy into chemical energy. Titanium dioxide has drawn extensive attention in this field owing to its high activity under UV light, good chemical stability, large availability, low price and low toxicity. However, the poor quantum efficiency derived from fast electron/hole recombination, the limited utilization of sunlight, and a weak reducing ability still hinder its practical application. Among the modification strategies of TiO2 to enhance its performance, the construction of heterojunctions with other semiconductors is a powerful and versatile way to maximise the separation of photogenerated charge carriers and steer their transport toward enhanced efficiency and selectivity. Here, the research progress and current status of TiO2 modification are reviewed, focusing on heterojunctions. A rapid evolution of the understanding of the different charge transfer mechanisms is witnessed from traditional type II to the recently conceptualised S-scheme. Particular attention is paid to different synthetic approaches and interface engineering methods designed to improve and control the interfacial charge transfer, and several cases of TiO2 heterostructures with metal oxides, metal sulfides and carbon nitride are discussed. The application hotspots of TiO2-based photocatalysts are summarized, including hydrogen generation by water splitting, solar fuel production by CO2 conversion, and the degradation of organic water pollutants. Hints about less studied and emerging processes are also provided. Finally, the main issues and challenges related to the sustainability and scalability of photocatalytic technologies in view of their commercialization are highlighted, outlining future directions of development.

Photothermal nano-confinement reactor with bimetallic sites for enhanced peroxymonosulfate activation in antibiotic degradation

In recent years, photothermal-assisted Fenton-like degradation of organic pollutants has become a prominent green method in environmental pollution control. Nevertheless, the design of suitable catalysts remains a significant challenge for this approach. Herein, zeolite-imidazolate framework-derived CoMn bimetallic nanoparticles embedded in hollow carbon nanofibers (CoMnHCF) have been developed as a photothermal nano-confinement reactor with multiple active sites to enhance reaction performance and promote peroxymonosulfate (PMS) activation. Under light irradiation, the local temperature within the porous spaces of CoMnHCF was significantly higher than the liquid temperature. The confined space concentrated heat, minimized thermal loss, and effectively utilizes this feature to activate PMS for antibiotic degradation. The results demonstrated that this system efficiently degraded various antibiotics, including tetracycline hydrochloride, levofloxacin, sulfamethoxazole, norfloxacin and chlorotetracycline. Photothermal contribution analysis revealed that thermal effects predominate in this system. Further DFT simulations explored the coordination environment of metal elements and the properties of related pollutants, predicting potential structures and reaction sites. A series of water quality experiments and cyclic tests demonstrated the system's significant application potential. This study offered new insights into advancing the integrated use of photothermal conversion and nano-confinement reactor activation of PMS in sewage purification.

Enhanced visible-light activation of persulfate for the removal of RhB by supported nano-(C,N,B)-tridoped TiO2/copper foam mixed-crystals

Photocatalytic persulfate activation by TiO2 and its application in sewage treatment have aroused great interest because of its high decontamination ability and strong adaptability, but the low light energy utilization rate and poor recycling of TiO2 limited its practical application. Herein, by using C-, N-, and B-modified TiO2 and immobilizing it on copper foam, we prepared a new and efficient (C,N,B)-TiO2/copper foam photocatalyst with enhanced visible-light activation performance of persulfate for the removal of RhB. It almost completely degraded RhB within 15 min of UV-vis light photocatalysis-assisted persulfate oxidation reaction with TOC removal of 53.17% in 30 min and presented the excellent long-term recyclability and stability, which is much better or comparative than those photocatalysts in the related literatures. (C,N,B)-TiO2/copper foam exhibited the largest apparent rate constant (0.149 min-1), 1.16 times higher than (C,N,B)-TiO2 (0.128 min-1), and 2.40 times higher than that of TiO2 (0.062 min-1), respectively. C,N,B doping modified the crystalline phase of TiO2, narrowed its band gap, and reduced charge-carrier recombination rate. These, together with the synergistic effect between photocatalysis and persulfate activation for enhancing generation of active species, jointly promoted the performance enhancement of TiO2. The 1O2 was the primary oxidation active species for the degradation of RhB, and the radical species (SO4•-, •O2-, and •OH) could further accelerate the photocatalytic activation of persulfate reaction.