Deepak Kumar Padhi

Fabrication of α-Fe2O3 Nanorod/RGO Composite: A Novel Hybrid Photocatalyst for Phenol Degradation

We report herein the fabrication of a hematite nanorod-graphene composite (α-Fe2O3 nanorod/RGO) via a facile template-free hydrothermal route with an aim to improve the photocatalytic efficiency of the α-Fe2O3 nanorod. The structural and morphological characterizations of the as-prepared composites were carried out using X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption, etc. The α-Fe2O3 nanorods were well-decorated on the surface of the graphene sheets, which helps in electron transfer from α-Fe2O3 to graphene and hence can delay the recombination process, leading to the improvement in photocatalytic activity. The composite containing 5 wt % RGO and α-Fe2O3 nanorods shows a 4-fold enhancement in the photocatalytic activity. The performance of photocatalytic activity was discussed in light of surface area, interaction between nanorods and graphene nanosheets, synergism between α-Fe2O3 nanorods and RGO sheets, light-harvesting properties of the composites, photoluminescence spectra, photocurrent measurement, and hydroxyl radical formation.

Facile fabrication of α-FeOOH nanorod/RGO composite: a robust photocatalyst for reduction of Cr(VI) under visible light irradiation

A facile one step hydrothermal route has been adopted for in situ deposition of α-FeOOH nanorods over reduced graphene oxide sheets (RGO) where sodium hydroxide plays a dual role in the growth of α-FeOOH nanorods and reduction of graphene oxide (GO) to RGO. The crystallographic, microscopic, and spectroscopic properties of the as-synthesized α-FeOOH nanorod/RGO composites were explored by XRD, Raman, DRUV-vis, PL, TRPL, XPS, FESEM, TEM, and photoelectrochemical measurement. The α-FeOOH nanorod/RGO composite displays superior photocatalytic activity towards the reduction of hexavalent chromium [Cr(VI)] compared with neat α-FeOOH nanorod under visible light irradiation. The extended π-conjugated flat 2D layer of graphene plays a crucial role in enhancing the photocatalytic activity of α-FeOOH nanorod by channelizing the photoexcited electrons on its surface. This leads to minimization of the electron–hole recombination which is successfully derived from photoluminescence study, time-resolved photoluminescence spectra, and photoelectrochemical measurement of α-FeOOH nanorod/RGO composites. The time resolved decay measurements showed longer average decay time (〈τ〉) for 3 wt% RGO loaded α-FeOOH of the order of 4.13 ns, than that of the neat α-FeOOH (2.536 ns). The improved photocurrent generation (nearly three times higher than that of the neat α-FeOOH nanorod) and low photoluminescence (PL) intensity of α-FeOOH nanorod/RGO composite is a result of the well decoration and strong attachment of α-FeOOH nanorods over RGO sheets, which significantly enhance its photocatalytic activity.

Enhanced visible light harnessing and oxygen vacancy promoted N, S co-doped CeO2 nanoparticle: a challenging photocatalyst for Cr(VI) reduction

Nanoceria and its derivatives are promising photocatalysts for environmental sustainability due to their strong redox ability, high oxygen storage/release capacity, eco-friendly nature, photostability and cost effectiveness. This study highlights the first time N/S co-doped ceria prepared using a simple hydrothermal method from a Ce(NO)3 and thiourea source. The spectrographic, crystallographic and macroscopic features of the as-synthesised photocatalysts were characterised by TEM, DRUV-vis, PL, TRPL, XRD, Raman and photoelectrochemical measurements. Under visible light illumination, doped ceria exhibits remarkable photocatalytic activity towards Cr(VI) reduction, in contrast to neat CeO2. The enhanced photoreduction ability of doped species, particularly 36 h treated samples (NCS-36), is due to more light absorption capacity, greater photocurrent generation and high concentration of photoexcited electrons, which were well supported by characterization techniques. The average lifetime decay of photoexcited electrons and the photocurrent density of NCS-36 were found to be 75.37 ps and 3.87 mA cm−2, which is nearly 3- and 12-times higher than that of neat ceria, respectively. These obtained results clearly explain the 93% photoreduction ability of NCS-36 towards a 50 ppm Cr(VI) solution within a time span of 120 min under visible light irradiation.

Visible-light-induced water reduction reaction for efficient hydrogen production by N-doped In2Ga2ZnO7 nanoparticle decorated on RGO sheets

This work presents an efficient in situ chemical method for constructing graphene-based N-doped In2Ga2ZnO7 nanocomposites (RGO/N-IGZ) for the production of hydrogen (H2) under visible-light irradiation. Well-anchored N-doped IGZ nanoparticles on RGO sheets were successfully obtained by the hydrothermal route that was employed. Several crystallographic, microscopic, and spectroscopic methods (XRD, DRUV-vis, PL spectra, TRPL analysis, XPS, TEM, and photoelectrochemical and photostability measurements) were adopted to study the robust photocatalytic activity of all the synthesised photocatalysts. A DRS study revealed that doping an IGZ nanoparticle with N reduced its band gap (Eg) from 2.50 eV to 2.34 eV and, furthermore, the introduction of RGO into the N-IGZ nanoparticle altered its Eg to 2.29 eV. The loading amount of RGO in an N-IGZ nanoparticle played a crucial role in enhancing the photocatalytic H2-producing ability of the N-IGZ nanoparticle. In the absence of a co-catalyst, a loading of RGO of only 2 wt% in N-IGZ enabled the production of the highest amount of H2, i.e. 726 μmol h−1, under visible-light irradiation. The superior photocatalytic activity of the 2RGO/N-IGZ nanocomposite in comparison with that of neat N-IGZ nanoparticles was demonstrated by correlation with the results obtained from BET surface area analysis, TEM, PL, TRPL, and photocurrent and photostability measurements, which concluded by showing better charge separation in the 2RGO/N-IGZ nanocomposite. 2RGO/N-IGZ exhibited low PL intensity, a longer average decay time (the values of for N-IGZ and 2RGO/N-IGZ were 2.11 and 7.11 ns, respectively), high photocurrent generation (42 times greater than that of N-IGZ), a large surface area and the production of the highest amount of H2 under visible-light irradiation without using any co-catalyst.