Dependence of the textural properties and surface species of ZnO photocatalytic materials on the type of precipitating agent used in the hydrothermal synthesis

Abstract

Three different precipitating agents (NaOH, NH 4 (H)CO 3 and CO(NH 2) 2) have been applied for the hydrothermal synthesis of ZnO powder materials, aiming at obtaining various types of porosity and surface species on ZnO. The synthesis procedures were carried out in the presence and in the absence of tri-block copolymer Pluronic (P123, EO20PO70EO20). These materials were characterized by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM)-energy-dispersive X-ray spectroscopy (EDX), BET method and TG-differential thermal analysis (DTA) method, and their photocatalytic activities were tested in the removal azo dye Reactive Black 5 (RB5). The urea precipitant yields spongy-like surface forms and the greatest share of mesopores. It has the highest specific surface area, highest degree of crystallinity of wurtzite ZnO phase and largest content of surface OH groups in comparison with the other two precipitants. The zinc hydroxycarbonate intermediate phase is missing in the case of NaOH as precipitating agent; therefore, it manifests poorer textural characteristics. The morphology of P123-modified sample is different and consists of needle-shaped particles. The urea-precipitated samples display superior performance in the photocatalytic oxidation reaction, compared with the other precipitated samples. The other two precipitating agents are inferior in regard to their photocatalytic activity due to greater share of micropores (not well-illuminated inner surface) and different surface morphologies.

Surfactant-assisted microwave processing of ZnO particles: a simple way for designing the surface-to-bulk defect ratio and improving photo(electro)catalytic properties

“…The textural properties of metal-oxide particles inuence their catalytic properties; more accurately, a larger surface area and a larger pore volume of the samples provided a larger number of active sites for photocatalytic reactions. 45 Different surfactants are oen used to control the morphology and texture of hydrothermally processed ZnO particles. [46][47][48][49] The inuence of surfactants on the textural properties of microwave processed zinc oxide particles are listed in Table 2.…”

“…A higher surface-to-bulk defect ratio diminishes the probability of recombination of photoexcited electrons and holes, simultaneously enhancing photocatalytic activity; while larger particles have a better absorption capacity. In the case of microwave processed ZnO particles, an excellent photocatalytic activity of ZnO/CTAB can be attributed to: (a) the larger surface area and larger pore volume (Table 2), providing a larger number of active sites for photocatalytic reactions, 45 (b) a specic platelike particle morphology with an average size of about 550 nm enhanced the absorption capacity of visible light, ZnO/CTAB particles exhibited $5% higher absorbance capacity than ZnO particles (Fig. 5), (c) the increased surface-to-bulk defect ratio (Fig.…”

Role of urea on the structural, textural, and optical properties of macroemulsion-assisted synthesized holey ZnO nanosheets for photocatalytic applications

“…Therefore, these results confirm that the amount of urea has a profound effect on altering the physicochemical and optical properties of ZnO. 69,70 The photocatalytic test shows that the ZnO_U0.5 sample has the highest photodegradation rate constant, k = (4.25 AE 0.08) Â 10 À3 s À1 , as well as a high photocatalytic efficiency of around 91.18%. The high photodegradation rate of this sample may be attributed to the synergistic effect of the holey sheet-like morphology, small crystallite size, high surface area, high density of defects, and small bandgap energy.…”

“…69 Specifically, a larger surface area and pore volume are beneficial for increasing the number of available active sites for various catalytic reactions. 70,71 The N 2 adsorption–desorption isotherms (Fig. 3c, f, i and l) of the ZnO products obtained with different urea to zinc precursor molar ratios display type III isotherms with type H3 hysteresis loop based on the IUPAC classification.…”

Modified Approach Using Mentha arvensis in the Synthesis of ZnO Nanoparticles—Textural, Structural, and Photocatalytic Properties

“…One of the most important applications of ZnO is in the field of heterogeneous photocatalysis for the removal of various organic pollutants in waste waters and air [17]. The UV irradiation of the semiconductor photocatalysts initiates a reaction by producing photoexcited electron-hole pairs, which can react further with the adsorbed pollutant molecules.…”