Visible-Light-Responsive Photocatalytic Activity Significantly Enhanced by Active [V_Zn+V_O⁺] Defects in Self-Assembled ZnO Nanoparticles

Abstract

Defect influences on the photoactivity of ZnO nanoparticles prepared by a powdered coconut water (ACP) assisted synthesis have been studied. The crystalline phase and morphology of ZnO nanoparticles were effectively controlled by adjusting the calcination temperature (400−700 °C). An induced transition of hybrid Zn 5 (CO 3 ) 2 (OH) 6 /ZnO nanoparticles to single-phase ZnO nanoparticles was obtained at 480 °C. The morphological analysis revealed a formation of ZnO nanoparticles with semispherical (∼6.5 nm)-and rod-like (∼96 nm) shapes when the calcination temperatures were 400 and 700 °C, respectively. Photoluminescence characterizations revealed several defects types in the samples with V Zn and V O + being in the selfassembly of semispherical-and rod-like ZnO nanoparticles. The photocatalytic activity of the ZnO nanoparticles was examined by assessing the degradation of methylene blue in an aqueous solution under low-intensity visible-light irradiation (∼3 W m −2 ). The results point toward the self-assembly of semispherical-and rod-like ZnO nanoparticles that had significantly better photocatalytic activity (∼31%) in comparison to that of spherical-agglomerated-or near-spherical-like species within 120 min of irradiation. The possible photocatalytic mechanism is discussed in detail, and the morphology-driven intrinsic [V Zn +V O + ] defects are proposed to be among the active sites of the ZnO nanoparticles enhancing the photocatalytic activity.

Evaluation of the Photocatalytic Activity of Distinctive-Shaped ZnO Nanocrystals Synthesized Using Latex of Different Plants Native to the Amazon Rainforest

“…The peaks could be indexed to the hexagonal structure of ZnO, belonging to the P63mc space group (ICSD#76641), without secondary phases. The crystalline domain shape and size estimated from XRD data by an SPH approach in parallel to the Rietveld refinement [4] predicted pitanga-like (D XRD = 15.8(4) nm (BA), teetotum-like (D XRD = 16.8(3) nm) (SA), and cambuci-like (D XRD = 22.2(5) nm) (SBA) shapes, as shown in 3D representation in the insets of Figure 1.…”

“…The bands positioned at 2877−3056 cm −1 and 2800−2877 cm −1 are due to stretching vibration of C−H related to alkenes and alkanes, respectively. These vibrations are explicitly linked to the presence of −CH 3 and −CH 2 , probably due to lipids and proteins [4,26] of the latex, which is common in plant extracts. The bands located at 1738, 1720, 1670, and 1650 cm −1 are associated with the carbonyl group and arise as a result of the existence of ester, aldehydes, carboxylic acids, and amides functional groups, respectively.…”

“…The morphology-controlled synthesis of metal oxide nanocrystals has gained much scientific interest because of their modulated physical properties induced by intrinsic defects associated with different morphologies [1,2]. Among them, ZnO has attracted more attention for its extensive applications in photocatalysts, ultraviolet blocks, and dye-sensitized solar cells [3][4][5][6]. ZnO is a semiconductor whose crystalline lattice can be easily engineered with different structural defects during crystal growth [7,8].…”

Porous ZnO Microspheres Grafted with Poly‐(N‐isopropylacrylamide) via SI‐ATRP: Reversible Temperature‐Controlled Switching of Photocatalysis**

“…[19][20][21] Studies have shown that the structure and morphology of ZnO, as a key factor, can significantly influence photocatalysis activities. [22][23][24] Recently, enormous efforts have been devoted to designing ZnO with various particles sizes and morphologies suitable for photocatalysis, including nanorods, [25] nanowires, [26] nanoribbons, [27] nanotubes [28] and three-dimensional (3D) ZnO micro/ nanostructures. [29] Especially, hierarchical 3D ZnO nanostructures are of significant interest since their novel architectural structures provide large surface area, [30] good permeability and high interfacial charge-transfer efficiency, [31,32] leading to the enhanced photocatalysis performance.…”

“…In particular, ZnO has received significant attention in wastewater treatment because of its promising photocatalysis performance for dye pollutants degradation [19–21] . Studies have shown that the structure and morphology of ZnO, as a key factor, can significantly influence photocatalysis activities [22–24] . Recently, enormous efforts have been devoted to designing ZnO with various particles sizes and morphologies suitable for photocatalysis, including nanorods, [25] nanowires, [26] nanoribbons, [27] nanotubes [28] and three‐dimensional (3D) ZnO micro/nanostructures [29] .…”