Chromic oxide nanoparticles (Cr2O3 NPs) are one of the notable inorganic NPs with outstanding features for several branches of modern science and technologies. Various fabrication approaches have been employed in the production of Cr2O3 NPs so as to meet its crucial potential. The ecological impacts and economic obstacles connected to most of the means of Cr2O3 NPs synthesis have contributed to the search for other alternative approaches with economic and environmental advantages. Surprisingly, the biological approaches to manufacturing using plant materials have been found suitable for the synthesis of Cr2O3 NPs dues to its myriad health, environmental, economic, and medicinal advantages. The important aspects of Cr2O3 NPs fabricated using plant broths and biomass augmented its application in antibacterial, antifungal, antioxidant, anticancer, antileshmanial, antiviral, and antidiabetic. In the area of electronics, chemistry and medicine, phytosynthesized Cr2O3 NPs have attracted tremendous usage in the fabrication of antibacterial, antifungal, antioxidant, anticancer, antileshmanial, antiviral, antidiabetic, photocatalytic agents as well as fabrication of microelectronic circuits, sensors, solar energy collectors and fuel cells. Notwithstanding, the enlisted advantages of biogenically produced Cr2O3 NPs, the challenges involved in the clarification of formation reaction still remain unsolved. This review presented the overview of the modern improvements in the synthesis, characterization methods, and applications of phytosynthesized Cr2O3 NPs in medicine, and pharmaceutical industries.

Environmentally friendly synthesis of Cr2O3 nanoparticles: Characterization, applications and future perspective ─ a review

Passive daytime radiative cooling inorganic-polymeric composite artificial lawn for the alternative to the natural lawn

Tuning of structural, optical, dielectric and transport properties of Fe-doped ZnO:V system

Chromium (III) oxide (Cr2O3) nanoparticles are generated by thermal treatment (calcination) of precursor materials such as chromium nitrate along with a poly (vinyl pyrrolidone) capping agent. The samples produced were characterised by various techniques, including X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). Examination results obtained from XRD showed that Cr2O3 nanoparticles exhibit hexagonal crystalline structures, with the presence of Cr and O in these novel materials being confirmed by results of analyses of both EDX and FT-IR. Results of TEM have pointed out that the average nanoparticle size was noticeably increased from 28 to 46 nm in relation to increase of calcination temperature of a range between 500 and 800 °C. The surface composition and valence state of the produced nanoparticles were examined by X-ray photoelectron spectroscopy (XPS), the optical energy gap has been evaluated using UV–visible reflectance spectra with the help of Kubelka–Munk equation. The energy band gap had a reversely proportional relationship with calcination temperature with a reduction in energy band gap from 3.12 to 3.01 eV. Photoluminescence (PL) spectra indicated an increase in photoluminescence with increasing particle size. The antibacterial activity of the Cr2O3 nanoparticles was evaluated in-vitro using gram-negative Escherichia coli ATCC 25922 and gram-positive Bacillus subtilis UPMC 1175.

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Comprehensive study on morphological, structural and optical properties of Cr 2 O 3 nanoparticle and its antibacterial activities

Tuning of structural, optical and toxicological properties of Gd3+ doped Yb2O3 nanoparticles

Preparation and structural, optical studies of Al substituted chromium oxide (Cr2O3) nanoparticles

Chromium oxide (Cr2O3) and Magnesium divalent ions (Mg2+) substituted Cr2O3 nanoparticles were synthesized by wet chemical method. In this report, we have investigated the influence of Mg2+ concentration on the structural and optical properties of Cr2O3 nanoparticles. XRD results demonstrated that pristine Cr2O3 nanoparticles exhibit rhombohedral structure and remains unchanged with Mg2+-substitution. However, it results in strained Cr2O3 nanoparticles with a decrease in lattice parameters and cell volume. The most intense peak centered around 534 cm−1 in Raman spectra depicted a considerable shift when Mg2+ is substituted at Cr3+ sites, complementing our XRD results. In addition, UV–Vis absorption investigation revealed marginal decay of optical band gap from 3 eV to 2.76 eV with the increase of Mg2+ concentration. Refractive index and Urbach energy have also been determined from the UV–Vis analysis and their values found to be increase with Mg2+-substitution.

Influence of Mg2+-substitution on the optical band gap energy of Cr2−xMgxO3 nanoparticles

Effect of structural and thermal disorder on the optical band gap energy of Cr2O3 nanoparticles

The present work is aimed to explore the microstructural and mechanical characteristics of coal-fly ash reinforced iron metal-matrix composites (IMMCs), synthesized through powder metallurgy technique. Coal-fly ash wt%, compacting load and sintering temperature were considered as the input variables, whereas sintered density and microhardness of the composites were taken as the output responses. Flowability and compressibility of the starting materials were demonstrated using Hausner ratio and Carr’s index. Decorous morphological, crystallographic and elemental characteristics of the starting materials and IMMCs were deliberated using Scanning electron microscopy, X-ray diffraction and Energy-dispersive X-ray spectroscopy investigations respectively. A significant improvement in the microhardness of IMMCs by 50% and drop in density by 35% were found at 15 wt% as compared to 0 wt% reinforcement. The substantial increase in the microhardness eventually resulted in an increase in their specific microhardness by a factor of two. 
Significant improvements in the microhardness of IMMCs at 15 wt % of reinforcement, compacted at 10 ton and sintered at 1150°C were found to be prompted by the strengthening mechanisms like load transfer, Hall–Petch effect and Taylor strengthening. The analytically calculated microhardness in the light of strengthening mechanisms was found smaller than the corresponding experimental values as a function of wt % of reinforcement. Further, statistical analysis of the obtained results was carried out using response surface methodology.

Vikram Verma

Papers

Preparation and structural, optical studies of Al substituted chromium oxide (Cr2O3) nanoparticles

Influence of Mg2+-substitution on the optical band gap energy of Cr2−xMgxO3 nanoparticles

Effect of structural and thermal disorder on the optical band gap energy of Cr2O3 nanoparticles

Investigations on microstructural and microhardness developments in sintered iron–coal fly ash composites

Role of Ni2+ substituent on the structural, optical and magnetic properties of chromium oxide (Cr2-xNixO3) nanoparticles