The utilization of biomass waste to produce valuable products has extraordinary advantages as far as both the economy and climate are concerned, which have become particularly significant lately. The large-scale manufacturing of agricultural waste, mainly rice by-products (rice husk, rice straw, and rice bran), empowers them to be the most broadly examined biomasses as they contain lignin, cellulose, and hemicellulose. Rice waste was first used to incorporate bulk materials, while the manufacturing of versatile nanostructures from rice waste at low cost has been developed in recent years and attracts much consideration nowadays. Carbon-based nanomaterials including graphene, carbon nanotubes, carbon dots, fullerenes, and carbon nanofibers have tremendous potential in climate and energy-related applications. Various methods have been reported to synthesize high-value carbon nanomaterials, but the use of green technology for the synthesis of carbon nanomaterials is most common nowadays because of the abundant availability of the starting precursor, non-toxicity, low fabrication cost, ease of modification, and eco-friendly nature; therefore, reusing low-value biomass waste for the processing of renewable materials to fabricate high-value products is remarkable. Carbon nanomaterials derived from rice waste have broad applications in various disciplines owing to their distinctive physicochemical, electrical, optical, mechanical, thermal, and enhanced biocompatibility properties. The main objective of this review and basic criteria of selecting examples and explanations is to highlight the green routes for the synthesis of carbon nanomaterials—i.e., graphene, carbon nanotubes, and carbon dots—from rice biomass waste, and their extensive applications in biomedical research (bio-imaging), environmental (water remediation), and energy-related (electrodes for supercapacitors, Li-ion battery, fuel cells, and solar cells) applications. This review summarizes recent advancements, challenges, and trends for rice waste obtained from renewable resources for utilization in the fabrication of versatile carbon-based nanomaterials.

Water pollution damages the aquatic environment due to the presence of organic contaminants, which in turn is distressing to the ecosystem. Photocatalytic activity is a greener and promising method to degrade these organic contaminants. In this research, we present the degradation of diverse water pollutants through zinc/iron oxide nanoparticles serving as photocatalysts. The photocatalyst was studied for its efficiency to photodegrade congo red, brilliant green and para nitro phenol. Moreover, it also presented an antibacterial activity against the bacterium E. coli. Photocatalyst was characterized via X-ray diffraction, scanning electron microscopy-energy dispersive X-ray spectroscopy, and fourier-transform infrared spectroscopy. Tauc plot was used to measure the optical band gap (1.84 eV). The effect of various parameters such as catalyst dose, contact time, dye dose/concentration and pH were also investigated to determine the optimum point of maximum degradation through response surface methodology. A face-centered composite design was used, and a quadratic model was followed by congo red, brilliant green dyes and para nitrophenol. The maximum photodegradation efficiencies were 99%, 94.3%, and 78.5% for congo red, brilliant green and phenol, respectively. Quantum yield for congo red, brilliant green and para-nitrophenol were 9.62 × 10⁻⁸, 1.17 × 10⁻⁷ and 4.11 × 10⁻⁷ molecules/photons, while the reaction rates were 27.1 µmolg⁻¹h⁻¹, 29.61 µmolg⁻¹h⁻¹ and 231 µmolg⁻¹h⁻¹, respectively.

Advanced water purification with excellent efficiency has been a significant challenge for humanity, and LaFeO₃-based perovskite semiconductors have been the subject of extensive research in recent years as promising candidates for efficient photocatalysts due to their stable structure and modifiable optoelectronic properties. However, the photocatalytic efficiency of LaFeO₃ perovskites is limited by rapid charge recombination, poor charge transport, and limited visible-light harvesting, all of which can impede the generation of active species. In this study, A/B-site Nd/Mn co-doping, nanostructure modulation, and CNTs integration were effectively merged as a multi-level engineering method to improve the optical response, electronic conductivity, and active surface area of LaFeO₃. The optimized 3% co-doping and 15% CNT contents enabled the final synthesized composite to exhibit excellent light harvesting due to a lower band gap, higher surface area, higher transient photocurrent, lower PL emission intensity, and good electrical conductivity. All these integrated features enabled the Nd/Mn-doped LaFeO₃ perovskite-CNTs nanocomposite to show 95% degradation of Brilliant Blue dye (BBD, 15 mg L^-1) in 1.5 h with a pseudo-first-order rate constant of 0.032 min^-1-triple that of pristine LaFeO₃. Mechanism study showed that superoxide radicals (˙O₂ ^-), which were formed via both conduction-band electron transfer and CNT-induced charge transfer, were the major reactive species for BBD degradation. Structural stability and the composite's reusability (up to six cycles with ∼97% activity after the conclusion of six cycles) indicate the suitability of the presented composite as a successful catalyst material.

This research work describes the synthesis of Ag-ZnO nanocomposites by combustion method using citrus clementina peels as an effective adsorbent material for removal of dyes. Water is an essential element for life. However, critical environmental issue of 20th century is water scarcity. Water has a wide-ranging effect on all aspects of human life, a serious hazard to public health and stability of food chain. Due to human activities the waste from our industrial, agricultural, and daily activities frequently pollutes the water. Therefore, there is an urgent need to develop cost effective and sustainable technologies for the removal of contaminants from waste water. The synthesized nanocomposites were characterized by (FTIR), UV Visible, (XRD) and (SEM). Then tested their potential toward efficient removal of Eosin Y and Congo-Red from waste water by using cost effective Adsorption method. Different parameters i.e., Dosage, Time, Concentration, pH and temperature have been studied. During Linear adsorption isotherm Langmuir and Temkin isotherms are best fitted on the adsorption of Dyes. Thermodynamic and kinetic studies have also done, while Pseudo 2nd order kinetic model showed better agreement as compared with other kinetic models. Thus synthesized Ag-ZnO Nanocomposites confirmed as excellent adsorbent material for waste water treatment.