ZnO on rice husk: A sustainable photocatalyst for urban air purification

Abstract

A cost-effective and sustainable De-NOx photocatalyst is prepared using zinc acetate and rice husk.ZnO@SiO 2 samples are obtained from the calcination of a homogenised precursor mixture at 600 C.ZnO nanoparticles (70 -180 nm) grow aggregated in spheres and well dispersed (40 -53 m 2 g -1 surface area) covering the silicon skeleton. The corresponding band gap for ZnO@SiO 2 photocatalysts was estimated at 3.1 -3.2 eV. When the samples are irradiated by sunlight in a nitrogen oxide atmosphere the NO  HNO 2  NO 2  NO 3 photochemical oxidation takes place. In comparison to unsupportedZnO and TiO 2 -P25, ZnO@SiO 2 samples exhibit high NO X removal values (70 %) and outstanding selectivity (> 90%), the latter related to the sensitivity of zinc oxide towards NO 2 gas. This new photocatalyst is easily recyclable and reusable.

Hydrothermally Grown ZnO Nanostructures for Water Purification via Photocatalysis

“…of concrete and local micro-turbulences [28][29][30]. The band gap variation could be caused by the morphological modifications of ZnO NSs, and could also be associated with their crystal quality, dislocations density, impurities, size, and thickness [30][31][32]. Indeed, nanosheets are supposed to contain more oxygen defects, which could reduce the band gap by acting as indirect donor energy levels below the conduction band [33][34][35].…”

Tailored Co3O4-Based Nanosystems: Toward Photocatalysts for Air Purification

“…5−12 Accordingly, several efforts have been undertaken to reduce NO emissions, especially in urban and industrialized areas. 1,3,13,14 In this context, photocatalytic technologies assisted by largely available natural resources, such as oxygen, water, and light, are low-cost and sustainable routes for NO degradation at ambient temperature. 8,10,15−20 These processes are initiated by the photoexcitation of suitable semiconductors, resulting in the generation of electron−hole pairs (e − /h + ).…”

“…The latter react with adsorbed water and oxygen molecules to yield highly reactive oxygen species [ROS; mainly hydroxide ( • OH) and superoxide radicals ( • O 2 − )], which, in turn, trigger NO x removal (De-NO x ; x = 1,2) by a sequential photo-oxidative process: NO → NO 2 − → NO 2 → NO 3 − . 1,2,8,18,21 Although various research works have been aimed at the development of De-NO x photocatalysts, 1,3,14 key problems still far from being completely overcome are related to the low activity and the generation of undesired/toxic byproducts, 1,5 in particular, the NO 2 intermediate. 6,13,20,22,23 Hence, an important goal to be fulfilled for an efficient NO x degradation, an actual open challenge, 2,4,10,[14][15][16]24 is the obtainment of a high selectivity toward harmless nitrates (NO 3 − ) as the major process products.…”

Tin as an Effective Doping Agent into ZnO for the Improved Photodegradation of Rhodamine B

“…Rhodamine B (C 28 H 31 ClN 2 O 3 ) is amongst the dyes used in textile, food, and water tracing in order to track water for the determination of its treatment capabilities, food industry and textile choice for the wide range of researchers [29][30][31] where photo catalysts are used to remove the pollutants in the presence of light source. ZnO is playing dominating role as photo catalysts [32][33][34][35] while compared to other catalysts like [36][37] due to its low cost, higher absorption efficiency than titania, easy to grow, high stability in thermal, chemical and physical environments [38][39][40] and is utilized in wide range of applications. Moreover, as it is a direct wide band gap material having 3.37 eV of band gap it finds applications like in LEDs, laser diodes, photovoltaic, semiconductor heterojunction, transparent conductors, and so on [41][42][43][44].…”