An Approach Towards Inactivation of Susceptible and Antibiotic Resistant Bacterial Contamination using Novel Photo–(electro)-catalysts

Water in most rivers in India does not meet the standards for drinking and even for bathing purposes due to the high concentration of coliforms, organic and inorganic contaminants. Overuse, uncontrolled release and careless disposal of drug, pharmaceutical components from hospital and domestic waste imparts a crucial role in developing a resistance towards antibiotics in microbes over a period of time. The class of bacteria affected by antibiotics are hereby called susceptible bacteria and the class that shows resistance towards antibiotics are known as antibiotic resistant bacteria. Therefore, presence of both class of microbes in water pose a serious question on the public health. The conventional ways to remove microbes possess the limitations of generating harmful by-products, fouling, high energy requirement and so on. In this regard, heterogeneous photocatalysis eliminates all the above-mentioned limitations by providing ease of separation, energy and cost benefits. However, there are some limitations associated with it such as recovery of the catalyst, reusability of the catalyst, photo-corrosion in the semiconductor material and so on. In this work, efforts have been made to rectify the issues associated with the use of photocatalysts at a larger scale. Semiconductor based photocatalysis possesses capability to facilitate surface redox reaction for generation of highly oxidizing and reducing radicals for mineralization of contaminants into non-harmful by-products as a result of absorption of photons. Commercially available catalysts such as TiO2, ZnO are wide band gap semiconductors and are highly efficient under UV irradiation. However, their wide band gap limits their viable usage in visible/ longer wavelength light. Due to limited access of UV wavelength from solar light (3-4 %), there is extensive need to design visible light responsive semiconductors or composites. Lowering the band gap, alteration in charge dynamics of the semiconductors and usage of novel lower band gap semiconductors are the ways to improve the photo response of the semiconductors. This study contains all the possible aspects of lowering of band gap by doping and charge dynamics alteration by band engineering with Type-1, Type-2 and Z-scheme. Metal substitution of Cu and interstitial doping of N in ZnO lattice and drastic improvement in optical properties were studied for inactivation of susceptible E. coli. Morphological aspect of the metal oxides is also a very crucial parameter in charge dynamics of the excitons, in this regard, ZnO/CdS/Ag nanorods and nanoparticles were synthesised to understand the photocatalytic mechanism involving surface plasmon effect due to the presence of Ag impregnation. Combined effect of doping and impregnation was also analysed by doping of Fe due effective coupling of orbitals due to its half-filled 3d orbitals. Ag is a widely used expensive antimicrobial agent. Therefore, CuO was introduced to increase the cost effectiveness with excellent photocatalytic properties. Leaching of metal ions from the semiconductor reduces the repeatability and stability of the catalysts. Therefore, metal free semiconductor C3N4 was coupled with CuWO4 in order to understand the Z-scheme mechanism of photocatalysis which is analogous to the photosynthesis. This Z-scheme composite was exploited for simultaneous inactivation of gram positive and gram-negative bacteria and extensive analysis of kinetics was studied for both the scenarios. These ways increase the charge separation and diffusion length and increases the carrier lifetime. However, recovery of these catalysts after usage is another concern which raise a question for this method to be commercialized. Also, the cost involved in the separation of catalysts in slurry form is another limitation which has been addressed in the present study. In order to address the problem of recovery and the separation of the catalyst particles in slurry form immobilization of the catalyst on substrates such as FTO, ITO, glass slide, cellulose acetate and so on can be performed. Vertically aligned ZnO nanorods coupled with CuI were grown on a conducting substrate (FTO) to augment the photo response in visible light. These substrates with grown catalysts were used as working electrodes for photo-electro-catalysis. A model was derived considering all the possible aspects of interaction of catalysts with the pollutants for various cases such as electrolysis, photolysis, electrocatalysis, photocatalysis and photoelectrocatalysis. Kinetics and mechanistic aspects of all the processes were touched and explored for simultaneous inactivation of drug (chloramphenicol) and susceptible/ antibiotic resistant bacteria (E.coli). The insights obtained from the above studies will be useful in better understanding of designing, synthesis and the charge dynamics of the semiconductor

Influence of copper oxide grown on various conducting substrates towards improved performance for photoelectrocatalytic bacterial inactivation

This paper analyzes the role of the conducting layer substrates (Cu and fluorine-doped tin oxide (FTO)) on grown copper oxide (CuO) in order to improve the performance of catalytic bacterial inactivation. Growth of CuO onto Cu substrate was via thermal oxidation of Cu whereas hydrothermal method was employed for CuO growth onto Fro. The surface morphology of CuO varied with respect to the substrates choice and epitaxy, developing particulated thin film and thin film consisting vertically aligned nanorods on Cu and FTO, respectively. Photo- and electro-based reactions were carried out to understand the effect of light, bias, bias-catalyst and light-bias-catalyst combinations, respectively, for the fast killing of E. coli. The experimental results showed a striking improvement in photoelectrocatalytic inactivation of E. coil using plain fabricated copper oxide substrate. The choice of conducting substrate material plays a crucial role in terms of both morphology controlled CuO growth under different facile methods and also governs the electron transfer efficiency to achieve an improved catalytic efficiency. The reaction mechanism was discussed by deriving an appropriate detailed model which is able to predict the experimental data in all the cases. This study gives an insight on energy saving and less carbon footprint approach for bacterial killing in a short interval. (C) 2017 Elsevier B.V. All rights reserved

Novel insights into the properties of AgBiO3 photocatalyst and its application in immobilized state for 4-nitrophenol degradation and bacteria inactivation

This study focuses on the synthesis of novel AgBiO3 nanoparticles by the hydrothermal route and investigating its properties responsible for waste water treatment. The temperature and time of hydrothermal reaction was optimized to 150 degrees C and 24 h to obtain highly active crystalline nanoparticles, as determined by XRD. The oxidation state of each element in the material was determined from XPS analysis. The morphology and size of the nanoparticles was obtained from SEM and TEM analysis. The optical and electrochemical properties of the material were studied by UPS and Mott Schottky plot. AgBiO3 was found to have a low band gap that facilitates the absorption of higher wavelength range as confirmed by Tauc plots and UV-vis DRS analysis. The excellent photocatalytic activity of the immobilized material towards the degradation of 4-nitrophenol and inactivation of E. coil was confirmed from kinetic studies and stability tests. A maximum degradation of 90% was achieved for 4-NP and a 5-log reduction was observed for viable E. coli cells in 5 h and 1 h respectively. Scavenger studies were performed to identify that superoxide radicals were responsible for the photocatalytic activity of the material. To eliminate the cost of separation and ease the reusability of the material, the nanoparticles were immobilized on cellulose acetate. Leaching of Ag and Bi ions from immobilized as well as free AgBiO3 nanoparticles into water was obtained via ICP-MS analysis. The results indicated that the leaching of Ag and Bi was controlled to a considerable extent due to immobilization on cellulose acetate matrix

Visible light driven efficient N and Cu co-doped ZnO for photoinactivation of Escherichia coli

Co-doping of a transition metal ion (Cu) and non-metal ion (N) on metal oxide substrate ZnO was achieved for the first time. The transition metal doping and N doping was carried out using combustion synthesis and a hydrothermal method, respectively. The combined effect of Cu and N doping was observed by varying the Cu percentage and keeping the nitrogen doping percentage constant. The catalysts were characterized by a wide variety of techniques. Incorporation of Cu and N in the ZnO matrix introduces sub energy bands near the conduction band and valence band, respectively and facilitates the absorption of longer wavelength spectra. These sub energy levels can also act as trapping sites for excitons. This results in reduced recombination and enhanced photocatalytic activity as confirmed by photoluminescence (PL). The photocatalytic inactivation of Gram negative bacteria (E. coli) was investigated using the N and Cu co-doped ZnO under UV and visible irradiation with different atom% of Cu. Kinetic analysis was used to obtain the order and rate constant of the inactivation reactions

Ag and CuO impregnated on Fe doped ZnO for bacterial inactivation under visible light

Interfacial coupling of semiconductor with metal has been demonstrated for inactivation of E. coli. Fe doped ZnO was synthesized by sol-gel method that resulted in enhanced absorbance in visible region. Various concentrations of Cu were impregnated on Fe doped ZnO that eventually turned into copper oxide and the photocatalytic activity of this material was compared with noble metal (Ag) impregnated on Fe doped ZnO. The obtained materials were characterized by various techniques. The crystal structures were determined by XRD and XPS was used to identify the oxidation states of the elements present in the photocatalyst. The morphologies and microstructures were determined by SEM. The optical absorbance of the photocatalysts was characterized by diffused reflectance spectra. Photocatalytic experiments were conducted for inactivation of E. coli using various catalysts. The rate constants obtained for 3 wt.% Cu impregnated Fe doped ZnO was higher than 1 wt.% Ag impregnated Fe doped ZnO. The higher photoactivity of these materials compared to pristine ZnO can be attributed to decreased recombination of the excitons in the synthesized photocatalysts that was validated by photoluminescence. This study indicates the possible employment of copper as a viable substitute for silver for anti-bacterial applications