Conducting Polymers and Photocatalysis: A Mini Review on Selected Conducting Polymers and Photocatalysts as TiO2 and ZnO

: This work covers a comprehensive mini review of the recent studies on the use of composites consisting of conducting polymers coupled with photocatalysts. The selected photocatalysts were TiO2 and ZnO and conducting polymers were polyaniline, polypyrrole and polythiophene. Based on the reference studies, preparation and characterization methodologies were presented along with reaction conditions. Assessment of photocatalytic performance of the composites was based on i. light intensity, band gap energy and effective wavelength region, ii. surface area and initial adsorption, iii. zeta potential and the pH of point of zero charges (pHzpc), with respect to selected substrate physico-chemical properties. Conclusive remarks covered recommendations for future studies to fulfill the misconceptions.

Reductive Dehalogenation – Challenges of Perfluorinated Organics

: In this mini-review, the problem of effective elimination of perfluorinated organic micropollutants from aquatic environment has been touched. The extraordinary chemical stability of common perfluorinated organic surfactants results in unsatisfactory efficiency of conventional treatment processes, which opens perspectives for photocatalytic methods - especially for reductive-dehalogenation. To tackle this challenge by photocatalysis one have to be aware of objective, physical limits set by very nature of the reduction process, electronic structure chemical stability, and formulation of the catalyst as well as emission characteristic of the light source. The paper provides some clues for rational design of reductive-dehalogenation oriented photolytic systems, which are derived on the basis of physical principles, and, rather sparse, experimental examples.

Ag-TiO2 Nanocomposites: visible or solar light driven plasmonic photocatalysis?

Background: The demand for photocatalytic processes assisted by solar radiation has stimulated the upgrading of established systems, as the semiconductor modification with noble metals. Objective: the synthesis, characterization, and photocatalytic activity evaluation of the Ag-TiO2, against sulfamethoxazole molecule, and investigate the significance of the plasmonic phenomenon in Visible (450 - 1000nm) and UV-Vis (315-800 nm) radiation. Methods: Different nanocomposites Ag/TiO2 ratios were synthesized by the deposition of Ag nanoparticles on the TiO2 surface by in-situ photoreduction, and then calcinated at 400°C for 2 hr. The chemical-physical properties of the materials were examined by UV-Vis Diffuse Reflectance (UV-Vis DRS) Scanning Electronic Microscopy (SEM), Transmission Electronic Microscopy (TEM), X-Ray Energy Dispersive Spectroscopy (EDS). The experiments were conducted in a cooled photochemical reactor irradiated by halogen lamp (250W). The degradation of Sulfamethoxazole was monitored by HPLC-DAD. Results: Although the prepared photocatalysts show an intense plasmonic band centered at 500 nm, no photocatalytic activity was observed in the process assisted by artificial visible radiation ( ≥ 450 nm). In processes assisted by artificial UV-Vis radiation, the photolysis rate of the model compound (sulfamethoxazole) was higher than the photocatalytic rate, and in the absence of UV radiation, all the reactions were inhibited. The positive effect of the presence of silver nanoparticles onto the TiO2 surface was only evidenced in studies involving solar radiation. Conclusion: The results suggest the need for a balance between UV and Vis radiation to activate the nanocomposite and perform the sulfamethoxazole degradation.

Bibliometric analysis of the research on photo-electrocatalysis and its possible application to wastewater treatment

Background: Possible applications of photoelectrocatalysis in the field of environmentally sustainable processes have inspired an exponentially increasing number of papers in the last decades. Less frequently, bibliometric analyses are presented, which are especially useful when a considerable amount of data is involved: metadata can be viewed from micro to macro perspective and may suggest ideas for future research. Objective: The objective of this study is to derive information on the research trends and to individuate possible gaps in specific topics, as well information on the authors and their related countries and institutes, and to quantify possible cooperation patterns between them. Methods: In addition to the classic data analyses immediately available on the database, such as the trend of the number of publications per year and the list of the most active authors or countries, the bibliometric analysis has been carried out using the VOSviewer software. Co-authorship and co-citation analyses have been performed, as well as co-occurrence of the keywords explicitly indicated by the authors. Results and Conclusion: Based on the publications in the SCOPUS database, the present work analysed the metadata relating to scientific articles published in the last two decades, dedicated to the research on photo-electrocatalytic processes and their possible application on wastewater treatment. Based on the list of the references present in the examined papers, the co-authorship analysis and the co-citation analysis also allowed the identification of the authors and the publications which have been most influential on the research on the examined topics. Indication has been obtained on the trend of the main topics investigated in time, as well as the current gaps in terms of content-wise and geographic cooperation.

Photocatalytic properties of TiO2 for the degradation of O3: Examined by environmental parameters

Background: This paper describes how environmentally relevant parameters affect titanium dioxide's photocatalytic properties (TiO2) to decompose ozone (O3). Methods: Thus, experiments have been carried out in a box chamber with TiO2 coated roofing membrane samples to determine the significance of light intensity, temperature, initial O3 concentration, and relative humidity. Furthermore, an outdoor experiment has been conducted where the roofing membrane was subjected to natural sunlight. Results: The results show a significant photocatalytic effect of TiO2. The half-life of the O3 decay curve is 5.8 min in near-ambient UV-light exposure compared with 7.1 min in dark conditions. Experiments conducted at higher light intensity show a more extensive degradation of O3, where the value of the reactive uptake coefficient increases from 0.044 to 0.051. Also, the measurements carried out under natural sunlight show a photocatalytic effect where the uptake coefficient value is 0.046. A larger photocatalytic effect is detected for the experiments conducted at 283 K and 303 K temperatures compared with experiments under standard conditions. Conclusion: Experiments carried out with a very high initial concentration of O3 show that 28.1 μg of O3 is decomposed than ambient conditions, where 2.3 μg is destroyed. This demonstrates that light intensity, temperature, ozone concentration, and relative humidity significantly impact TiO2's degradation of O3.

Degradation of the o-phenylphenol fungicide in water by unconventional CeO2-WO3 photocatalysts

Background: Water pollution due to emerging contaminants such as pesticides, pharmaceutics and/or plasticizers, is a serious environmental problem strictly connected to the safety of human and ecosystem life. For this reason, the development of high-performing (photo)catalysts for water purification is crucial. Objective: In recent years, the synergistic effects in Advanced Oxidation Processes (AOPs) can perform better strategies to remove recalcitrant contaminants from water. In this contest, the (photo)catalytic activity of CeO2-WO2materials for the degradation of the orto-phenylphenol fungicide comparing the photocatalytic, the Fenton and the photo-Fenton-like processes, has been examined. Methods: The samples were synthetized through deposition-precipitation mediated with the hexamethylenetetramine (HMTA) surfactant. The chemico-physical properties of the materials were examined by Raman, UV-Vis Diffuse Reflectance (Uv-vis DRS) and X-Ray photoelectron (XPS) spectroscopies, N2 adsorption-desorption measurements and transmission electron microscopy (TEM). The (photo)catalytic measurements were made through a home-made photoreactor irradiated by a solar lamp. The degradation of the fungicide was measured by UV-vis spectroscopy. Results : An efficient heterojunction was formed between the CeO2 and the WO2 oxides, which provided a good degradation percentage of the pesticide (65%) employing the solar photo-Fenton-like reaction that was the best performing process among the three investigated AOPs. The addition of WO3on CeO2 facilitated the ionic exchange between the Ce and the W ions, boosting the redox properties of cerium oxide. Conclusions: The strong interaction between CeO2 and WO3 and the peculiar properties of this unconventional composite pave the way to its use as a promising material for water depollution.

Research progress over Cu2O/n-type semiconductor composites in photocatalysis

: Photocatalysis is a feasible technology to solve energy shortage and environmental pollution by using solar energy. Semiconductor photocatalysts with low cost, high stability and environmental friendliness are demonstrated advantages for the production of solar fuel, CO2 reduction, and degradation of pollutants. Among them, Cu2O presents numerous potential for photocatalysis because of its narrow bandgap and high activity under visible light. However, the rapid recombination of photoinduced electron-hole pairs and the instability of Cu2O under light irradiation limit its photocatalytic performance. In order to solve the above issues, researchers prefer to incorporate Cu2O with n-type semiconductors to design p-n heterojunction composites, thus regulating the band structure, promoting the separation and transfer of electrons and holes, and accelerating the redox reaction onto the surface. In this manuscript, the preparation methods of Cu2O/n-type semiconductor composites such as hydrothermal method, electrodeposition method, and in situ method are concluded, the photocatalytic applications including CO2 reduction, hydrogen production, and degradation are presented, and the catalytic mechanism like Z-scheme, p-n heterojunction, etc. are discussed, respectively. This review also proposes that there are still challenges in broadening the photocatalytic application of Cu2O/n-type semiconductor composites.

CdS-Based Photocatalysts for Solar Water Splitting

: Photocatalytic water splitting for hydrogen production is a promising pathway for solar energy convention into chemicals. Among various semiconductor-based photocatalysts, cadmium sulfide (CdS) attracted extensive attentions due to the narrow band gap nature (2.4 eV) for efficient visible light absorption, suitable band position for water splitting, and outstanding photocatalytic activity. In this review, we summarize the recent advances for the synthesis of CdS, and modification strategies including heteroatom doping, loading cocatalysts, and hetero/homo-junction fabrication are also presented. Moreover, a brief perspective and challenges on CdS-based photocatalyst are also discussed.