Evolution of (a) relative concentration of rhodamine B (RhB) and (b) CH4 production as a function of UV irradiation time. XZNY is the N-doped ZnO, where X is the temperature (°C) and Y is the time ...(h) of the heat treatment; ZP is the undoped ZnO.
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•Synthesis of N-doped ZnO nanoparticles, using urea as nitrogen source.•Photocatalytic performance was influenced by the synthesis conditions.•N-doped ZnO nanoparticles were versatile photocatalysts in redox reactions.
N-doped ZnO is a prospective material for photocatalytic reactions. However, only oxidative paths are well investigated in the literature. This paper describes a comparative study about ZnO and ZnO:N potential for oxidative and reductive reactions, probed by rhodamine B dye photodegradation and CO2 photoreduction. The materials were prepared by the polymeric precursor method, using urea as a nitrogen source, and different heat treatments were used to observe their effects on surface decontamination, crystallinity, particle sizes and shapes, and photocatalytic performance. ZnO and ZnO:N presented a wurtzite crystalline structure and nanometric-scale particles. Samples submitted to higher temperatures showed lower specific surface areas, but higher crystallinity and lower contents of species adsorbed on their surfaces. On the other hand, the photocatalysts annealed in shorter times presented smaller crystallite sizes and lower crystallinity. These factors influenced the photoactivity in both conditions, i.e., oxidation and reduction reactions, under the ultraviolet and visible light, indicating that structural factors influenced the adequate charge separation and consequent photocatalytic activity since the as-synthesized samples were versatile photocatalysts in both redox reactions.
•Heterostructures were more actives than commercial TiO2 nanopowders.•Synthesis method influence on the semiconductor photoactivity.•Interface between the oxides was the main factor to photoactivity ...per area unit.•Attack by OH radical was the main photodegradation mechanism.•Surface OH groups are correlated to the photocatalytic efficiency.
This paper describes the synthesis of TiO2-SnO2 heterostructures and their application to water decontamination based on the photodegradation of Rhodamine B (RhB). The heterostructures were fabricated through two different routes, a hydrolytic sol gel and the polymeric precursor method, both of which induced the growth of SnO2 on commercial TiO2. The results show that the heterostructures presented higher photoactivity behaviors than commercial TiO2 nanopowders. The achievement of homogeneity during phase formation (i.e., of the SnO2 dispersion over the TiO2 nanoparticles) was a key parameter for obtaining higher photocatalytic activities per unit area. The main degradation mechanism was correlated with the process of OH radical generation, which was related to the concentration and nature of the surface hydroxyl groups. Accordingly, the polymeric precursor method was shown to be more adequate for dispersing higher amounts of SnO2 in comparison with the hydrolytic sol gel method. Additionally, the polymeric precursor method delivered higher proportions of bonded surface hydroxyl groups, which were responsible for radical formation; in contrast, the hydrolytic sol gel method demonstrated the highest amount of adsorbed water.
This research investigated the production of porous zinc oxide (ZnO) ceramics obtained by the replica method for water depollution by photocatalytic processes. Five photo-decolorization cycles were ...performed to analyze the reuse potential of the ceramics. Statistical analyses using R programming were conducted to investigate possible significant differences between them. The ceramics porosities were between 46.74 and 62.50% (depending on the composition). The most successful results were achieved in prepared ceramics from slurries containing 65% ZnO and 1% carboxymethylcellulose, in which the dye decolorization results reached 90.5% after 5 cycles, indicating a high reuse potential of these ceramics. Multivariate analysis proved the negative effect of increasing the heat treatment temperature on the evaluated properties. The best processing conditions to obtain porous ZnO ceramics by the replica technique were established through statistical tools, with very satisfactory results in the photo-decolorization potential of the investigated dye.
Three different synthesis methods were applied to obtain TiO
2
nanoparticles: microwave-assisted hydrothermal (TiO
2
-MW), sonochemical (TiO
2
-US), and polymeric precursor (TiO
2
-PP). The ...nanoparticles thus obtained presented 93% (TiO
2
-MW) and 92% (TiO
2
-US) anatase phase, and TiO
2
-PP 93% rutile phase. The TiO
2
-US sample performed best during the Prozac® photodegradation assays because of its lipophilic surface, attributable to the C-H groups therein. Additionally, adsorption rate and photodegradation were optimized by adjusting Prozac® solution to pH ~ 8. Following Prozac® photodegradation, quantitative monitoring of its by-products (PPMA, MAEB, and TFMP) was done using HPLC. This quantitative approach led us to conclude that semiconductor photoactivity cannot be discussed solely in terms of the main compound. Lastly, it was seen that these by-products compete with each other in the degradation mechanisms and are influenced by different materials.
Graphical abstract
This study aimed to investigate the kinetics, isotherms, and thermodynamics of biosorption of the cationic dye rhodamine B by a low-cost biosorbent prepared from
Aspergillus oryzae
cells. Culture ...medium composition (mineral salts, nitrogen source, and carbon source) influenced removal efficiency, and dye removal increased with increasing biosorbent concentrations until a plateau was reached at 10 g L
−1
. Temperature and dye concentration were directly related to removal, and the highest removal efficiency was obtained at 40 °C and 200 mg L
−1
of dye. The adsorption kinetics was best fitted to a pseudo-second-order model, and equilibrium data were well described by the Freundlich equation. Thermodynamic analysis indicated that the biosorption of rhodamine B by
A. oryzae
cells is physical in nature, spontaneous, and more favorable at higher temperatures and dye concentrations. Overall, the results suggest that inactivated
A. oryzae
biomass is a promising biosorbent for the removal of cationic dyes from wastewater.
Commercial TiO
2
nanoparticles were superficially modified through polymeric resins obtained from polymerization of citrate complexes of Y
3+
and Al
3+
with ethylenglycol. The materials were treated ...at 450 °C for 4 h to obtain modified nanoparticles, which were characterized by HR-TEM, Zeta potential and surface area through N
2
fisisorption. Rhodamine B photodegradation by visible light irradiation and in presence of those modified nanoparticles was compared with the same process in presence of unmodified commercial TiO
2
nanoparticles. It was observed, by UV–visible spectroscopy, that the catalytic photoactivity in presence of modified nanoparticles was smaller than that observed with commercial TiO
2
nanoparticles. However, the surface modifier played an important role in the photodegradation kinetic process, showing a non-linear relation between modifier amount and photodegradation rate, presenting a maximum value at 0.8% (w/w).
Tin dioxide nanoparticle suspensions were synthesized at room temperature by the hydrolysis reaction of tin chloride (II) dissolved in ethanol. The effect of the initial tin (II) ion concentration, ...in the ethanolic solution, on the mean particle size of the nanoparticles was studied. The Sn2+ concentration was varied from 0.0025 to 0.1 M, and all other synthesis parameters were kept fixed. Moreover, an investigation of the effect of agglomeration on the nanoparticle characteristics (i.e., size and morphology) was also done by modifying the pH of the SnO2 suspensions. The different samples were characterized by transmission electron microscopy, optical absorption spectroscopy in the ultraviolet range, and photoluminescence measurements. The results show that higher initial ion concentrations and agglomeration lead to larger nanoparticles. The concentration effect is explained by enhanced growth due to a higher supersaturation of the liquid medium. However, it was observed that the agglomeration of the nanoparticles in suspension induce coarsening by the oriented-attachment mechanism.
This paper describes the development of ZnO nanoparticles by a chemical method, to test them in the photocatalysis of the degradation of textile dyes, using Rhodamine B (RhB) as a probe reaction. The ...samples were submitted to different heat treatments in order to observe the annealing effects on the photocatalytical properties, surface decontamination and the consequent particle change, in terms of crystallinity. The as-prepared samples (ZOA) correspond to a metastable phase (oxy or hydroxy zinc acetate) and post annealing leads to ZnO crystallization. In spite of the XRD patterns showing only the ZnO phase for heat treatment at 100 degrees C, FTIR data show that carboxylate groups remains attached to the ZnO surface up to 300 degrees C. Up to 300 degrees C the presence of these carboxylate groups, provided by the synthesis method, showed to be more relevant to photoactivity than the specific surface area. At higher temperatures, crystallinity becomes the dominant factor and an increasing of crystallinity favors the photoactivity.
This work described the acquisition of immobilized ZnO semiconductors using the slip casting technique, for application as reusable photocatalysts in the degradation of Rhodamine B. The influence of ...the heat treatment temperature (800°C, 900°C, and 1000°C) on the physical, thermal, microstructural, and photocatalytic properties was investigated. All samples presented the wurtzite crystal structure, and the surface was completely absent of organic matter residues. The samples presented band gap values around 3.2 eV. The ones heat treated at 800°C showed lower density (3.40 g/cm3, corresponding to 60% of the ZnO theoretical density), smaller average grain size, in addition to higher apparent porosity (around 40%). These characteristics provide better photocatalytic activity to the sample heat treated at 800°C, since it promoted 92.2% dye degradation, while samples heat treated at 900°C and 1000°C promoted 81.8% and 54.2% dye degradation, respectively. The integrity of all samples was maintained after the photocatalytic tests. Thus, the reuse capability of the sample with the best photocatalytic performance, that is, the sample heat treated at 800°C, was evaluated in six cycles of photocatalysis. The sample proved to be reusable, promoting degradation of practically 100% of the dye after the third cycle of reuse.
Photocatalytic processes have been applied to treatment of organic effluents through the mineralization of these pollutants on a semiconductor surface. Obtaining nanosemiconductors is desirable for ...the increasing of particle surface area and improvement in photocatalytic efficiency. In this paper, it was evaluated the influence of High Energy Milling (HEM) as a technique to produce nanocrystalline zinc oxide. The photocatalytic activity of the milled powders to degrade Rhodamine-B dye when exposed to ultraviolet and visible radiation also was investigated. The powders were milled during 4 and 10 hours by dry media milling and 10 hours by wet media milling. The results indicated that there were no detectable powder contamination during the millings and the reduction of crystallite size was function of time and media of milling. All of the assessed samples demonstrate high degradation of the dye, which corroborates with the potentiality of this technique to photocatalysts production. The material milled during 10 hours by dry media milling showed the best results under the experimental conditions.
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