APPLICATIONS OF PLASMONIC AND METAL-SEMICONDUCTOR COMPOSITE NANOPARTICLES

Au-ZnO based UV photocatalysts of two different morphologies: (i) Au core - ZnO shell and (ii) Au-decorated ZnO nanorods were prepared and demonstrated for efficient degradation of different dyes and their mixtures. Core-shell nanoparticles have better dispersabilty over ZnO nanorods. However, the former requires annealing for improved efficiency.

A. Au-ZnO core-shell nanoparticle photocatalyst:

• Au cubic nanoparticles as core with ZnO shell layer were grown for photocatalysis applications.
• Preparation method: Seed mediated growth of Au cube nanoparticles followed by ZnO shell layer (Fig. 6) growth by hydrothermal method.
• Crystalline quality and dye degradation efficiency of these nanoparticles were improved after annealing above 400 oC temperature (Fig. 6).



Fig. 6 Electron microscopy images of (a) cubic Au and (b) Au-ZnO core-shell nanoparticles and (c) variation of methylene blue dye absorbance with UV irradiation time in presence of annealed core-shell nanoparticles.



• Photocatalytic dye degradation was optimized with respect to: nanoparticles quantity, dye concentration, nature of dye, solution pH and concentration of different scavengers.
• These nanoparticles are efficient photocatalyst with ≥ 95% dye degradation efficiency for two hours of low power UV lamp irradiation up to 20 mg/L dye concentration (Fig. 7).

Fig. 7 Au-ZnO core-shell nanoparticles as UV photocatalyst for removal of dye from aquuous solution



• Better dispersabilty, economic and scalable growth method of these nanoparticles along with low power UV lamps are promising for its application towards treatment of colored waste water discharge /effluents, degradation of phenolic compounds and other organic molecules.

Publications:

1. Shweta Verma et al., Journal of Environmental Engineering, 103209, 2019, 1-13
2. Shweta Verma, B. Tirumala Rao et al, Proc. DAE-BRNS National Laser Symposium-NLS 24, 2015, RRCAT, Indore.

• High crystalline Au-ZnO photocatalyst for degradation of different dyes, binary dye mixtures and two different industrial effluents.
• Preparation method: Hydrothermal growth of ZnO nanorods and photo-mediated deposition of Au nanoparticles over ZnO (Fig. 8).



Fig. 8 Scanning electron microscope image of Au nanoparticle decorated ZnO nanorods with its photograph in inset (left) and variation of degradation efficiency with number of cycles of photocatalyst used (right).



• Photocatalytic treatment resulted in dye de-coloration along with considerable decrease of chemical oxygen demand (COD) of dye solution, promising for water reusability.
• Photocatalyst is efficient for treatment of mixed dyes (Fig. 9), effluents and pH dependent degradation rate decides either selective or simultaneous degradation of mixed dyes.



Fig. 9 Photographic image of mixed binary solutions of different dye combinations (each of 30 μM concentration) with increasing irradiation time of 120 min. from left to right at 12 pH condition. MB: methylene blue; MO: methyl orange; Rh6G: Rhodamine 6G; RhB: Rhodamine B.



• A small-scale double-wall photo-reactor (Fig. 10) has been fabricated for UV-light photocatalytic applications.



Fig. 10 Photographic image of double wall UV photo-reactor



• These nanoparticles are also shown to be effective for photocatalytic treatment of two industrial effluents (Fig. 11) from local textile and pharmaceutical industries.



Fig. 11 Photographic image of (a) textile and (b) pharmaceutical effluent before (left) and after (right) 140 min. of UV irradiation in presence of UV photo-catalyst.




Fig. 12 Absorption spectra of (a) textile and (b) pharmaceutical effluent showing continuous decrease in absorbance with irradiation time in presence of photo-catalyst.

Publications: Shweta Verma et al., Ceramic International, in press, 2021, doi: https://doi.org/10.1016/j.ceramint.2021.09.014.

• Silver phosphate nanoparticles were prepared and shown to be highly effective as visible light photocatalytic degradation of dyes.
• Preparation method: Co-precipitation chemical method for scalable growth of different shapes of silver phosphate nanoparticles (Fig. 13).



Fig. 13 Scanning electron microscope images of silver phosphate nanoparticles of different shapes.



• These nanoparticles are efficient photocatalyst with ~ 100% dye degradation efficiency within ~30 minutes of solar irradiation for various dyes upto 20 mg/L concentration.



Fig. 14 Variation of absorbance of methylene blue dye (15 mg/L) at different interval of solar light irradiation



• These nanoparticles were also found to be efficient for treatment of pharmaceutical effluents under sun light irradiation of 2 hrs (Fig. 15).



Fig. 15 Photographic image of pharmaceutical effluent before and after 120 min. of sun light irradiation in presence of silver phosphate nanoparticles.



• A flowing water type solar photo-reactor has been fabricated for treatment of relatively large quantity of effluents under sun light irradiation (Fig.16).



Fig. 16 Photographic image of in-house developed flowing water type solar photo-reactor for water treatment application.



• • Tin sulfide nanoparticles based visible active photocatalyst was also prepared for photocatalytic reduction of carcinogenic Cr(VI) ions in aqueous solutions (Fig. 17). This would be beneficial for ecofrienldy treatment of electroplating discharge water effluents containg Cr(VI) ions.



Fig. 17 Photographic image of potassium dichromate: Cr(VI) solution of ~ 300 nM concentration before and after ~ 4 hrs of visible light irradiation in presence of tin sulfide nanoparticles.