Semiconductor photocatalysts: A critical review highlighting the various strategies to boost the photocatalytic performances for diverse applications.

The photocatalytic technology illustrates an eco-friendly and sustainable route to overcome environmental and energy issues. The successful construction of a photocatalyst depends on four key elements: light absorption ability, the density of active sites, redox capacity, and photoinduced electron-hole recombination rate. Sincemost of intrinsic semiconductor photocatalysts cannot meet all these requirements, they are often modified to boost their photocatalytic properties. Many strategies have been adopted to design novel and efficient photocatalysts for diverse applications. Herein, we review the most efficient of these strategies and methods focused on effectively overcoming the efficiency limitations of photocatalysts to promote their large-scale application. Subsequently, a particular aim is put on the most current studies for photocatalytic applications, including CO2 reduction, N2 fixation, H2 evolution, and pollutants degradation. Finally, key challenges and future perspectives in designing and implementing semiconductor photocatalysts for large-scale applications are discussed. Therefore, it is foreseen that this review will work as a guide for future research and provides a variety of strategies to develop novel and high-performance photocatalysts for various applications.

Novel Nd-N/TiO2 Nanoparticles for Photocatalytic and Antioxidant Applications Using Hydrothermal Approach.

In this study, photocatalysis was employed to degrade a wastewater pollutant (AB-29 dye) under visible light irradiation. For this purpose, nitrogen (N)- and neodymium (Nd)-doped TiO2 nanoparticles were prepared using the simple hydrothermal method. X-ray diffraction (XRD) revealed an anatase phase structure of the Nd-N/TiO2 photocatalyst, whereas properties including the surface morphology, chemical states/electronics structure and optical structure were determined using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-visible (UV-vis.) and photoluminescence (PL) spectroscopies. Photocatalytic testing of the prepared nanomaterials was performed to remove acid blue-29 (AB-29) dye under visible-light exposure. The prepared Nd-N/TiO2 nanoparticles demonstrated a superior photocatalytic activity and the decolorization efficiency was about 92% after visible-light illumination for 1 h and 20 min, while N/TiO2, Nd/TiO2 and TiO2 only showed a 67%, 43% and 31% decolorization efficiency, respectively. The enhanced photocatalytic activity of the Nd-N/TiO2 photocatalyst was due to a decrease in the electron/hole's recombination and the increased absorption of TiO2 in the visible range. The reusability results showed that the average photocatalytic activity decrease for all the samples was only about 16% after five consecutive cycles, indicating a good stability of the prepared nanomaterials. Moreover, the radical scavenging activity of the prepared nanomaterials was evaluated using the DPPH method. The novel Nd-N/TiO2 exhibited a higher antioxidant activity compared to all the other samples.

Facile synthesis and antimicrobial activity of CdS-Ag2S nanocomposites.

In this study CdS-Ag2S nanocomposites for antibacterial activity were synthesized via facile co-precipitation method using PVP as capping agent. The prepared nanocomposites have particle sizes in the range of 50-100 nm (SEM) and PVP addition has good influence on the morphology of nanocomposites. The antimicrobial activity of pure Ag2S, CdS and CdS-Ag2S composites was evaluated against Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli. The results demonstrate that antibacterial activity was significantly improved due to increasing ratio of CdS into CdS-Ag2S nanocomposites in comparison to pure Ag2S and CdS.

Visible light sensitive Ag/TiO2/graphene composite as a potential coating material for control of Campylobacter jejuni.

Infectious diarrhea caused by the food borne pathogen, Campylobacter jejuni, is a major threat to public health worldwide leads high incidence of child mortality each year. In the present study, hydrothermal synthesis of Silver-Graphene-TiO2 nanocomposites along with TiO2, TiO2-Graphene and TiO2-silver nanocomposites was done and the samples were characterized using X-ray diffraction (XRD), tunneling electron microscopy (TEM) and UV-Vis Spectroscopy. Effect of silver and graphene addition on the broad spectrum antibacterial ability of TiO2 was studied under visible light. Moreover, the effects on bacterial survival, membrane integrity, cellular motiltiy and biofilm formation of C. jejuni were also evaluated. A synergetic effect of silver and graphene on Silver-Graphene-TiO2 nanocomposites was observed as indicated by its increased visible light sensitivity and enhanced antibacterial activity under visible light compared to its parent derivatives. Silver-Graphene-TiO2 composites effectively reduced growth and caused leakage of protein and DNA from C. jejuni cell. Atomic Force Microscopy was used to confirm bacterial cell damage. Besides, it also reduced motillity, hydrophobicity and autoaggregation of C. jejuni and showed excellent inhibition of biofilm formation. Furthermore, no significant cytotoxicity of synthesized nanoparticles was observed in human cell lines. We propose that Silver-Graphene-TiO2 composites can be used as effective antimicrobial agents to control the spread of C. jejuni by preventing both bacterial growth and biofilm formation.

Photocatalytic, sonocatalytic and sonophotocatalytic degradation of Rhodamine B using ZnO/CNTs composites photocatalysts.

A series of ZnO nanoparticles decorated on multi-walled carbon nanotubes (ZnO/CNTs composites) was synthesized using a facile sol method. The intrinsic characteristics of as-prepared nanocomposites were studied using a variety of techniques including powder X-ray diffraction (XRD), high resolution transmission electron microscope (HR-TEM), transmission electron microscope (TEM), scanning electron microscope (SEM) with energy dispersive X-ray analysis (EDX), Brunauer Emmett Teller (BET) surface area analyzer and X-ray photoelectron spectroscopy (XPS). Optical properties studied using UV-Vis diffuse reflectance spectroscopy confirmed that the absorbance of ZnO increased in the visible-light region with the incorporation of CNTs. In this study, degradation of Rhodamine B (RhB) as a dye pollutant was investigated in the presence of pristine ZnO nanoparticles and ZnO/CNTs composites using photocatalysis and sonocatalysis systems separately and simultaneously. The adsorption was found to be an essential factor in the degradation of the dye. The linear transform of the Langmuir isotherm curve was further used to determine the characteristic parameters for ZnO and ZCC-5 samples which were: maximum absorbable dye quantity and adsorption equilibrium constant. The natural sunlight and low power ultrasound were used as an irradiation source. The experimental kinetic data followed the pseudo-first order model in photocatalytic, sonocatalytic and sonophotocatalytic processes but the rate constant of sonophotocatalysis is higher than the sum of it at photocatalysis and sonocatalysis process. The sonophotocatalysis was always faster than the respective individual processes due to the more formation of reactive radicals as well as the increase of the active surface area of ZnO/CNTs photocatalyst. Chemical oxygen demand (COD) of textile wastewater was measured at regular intervals to evaluate the mineralization of wastewater.