Clinoptilolite supported rutile TiO 2 composites were synthesized for the enhancement of its photocatalytic performance in the degradation of the aqueous terephthalic acid solution under UVC illumination by the increase in its surface area and to simplify its recovery from the treated solution after use. The XRD spectra of the composites revealed the formation of pure rutile TiO 2 on the surface of the clinoptilolite. The SEM images showed the formation of the spherical TiO 2 clusters were composed of nano fibers on the surface of the clinoptilolite. For all composites synthesized, the dispersion of the TiO 2 particles on the clinoptilolite led to a surface area larger than that of the bare TiO 2 and clinoptilolite. The materials synthesized in the present study exhibited higher catalytic activity compared with the commercial Degussa P25 and anatase. Among the catalysts synthesized the TiO 2 /clinoptilolite with a weight ratio of 0.5 was found to be the most photoactive catalyst even though it contains a lesser amount of active TiO 2 . The kinetic of the reactions for different catalyst was found to be consistent with the pseudofirst order kinetic model. The results of the Langmuir-Hinshelwood model showed the slight contribution of the adsorption on the degradation. The activity of the TiO 2 /clinoptilolite with a weight ratio of 0.5 decreased after repetitive use due to the accumulation of the TPA molecules on the surface of the catalyst.
The adsorptive removal of cefdinir, an antibiotic, from aqueous solutions on TiO2, SiO2 and TiO2/SiO2 nanostructures was studied by batch experiments. The SiO2 particles were obtained from rice husk ash. Investigated were the effects of the solution pH, adsorbent dosage, initial adsorbate concentration, and solution temperature on both cefdinir uptake and removal. The studies suggest that the adsorption of cefdinir on the nanostructures was mainly due to the electrostatic interaction between the ionic adsorbate molecules and charged adsorbent surface sites. The adsorption isotherm data of TiO2 and SiO2 fit well to the Langmuir isotherm model and the Freundlich model for TiO2/SiO2. The thermodynamic studies indicated favorable and spontaneous occurrence of adsorption. The kinetic data of TiO2 fitted best with PSO reaction model equation, and was described well by Weber-Morris diffusion model with dominating control mechanism of intraparticle diffusion and limited contribution of internal film diffusion.
To synthesize nano-sized TiO 2 , two different methods, namely thermal hydrolysis (TH) and reverse micelles as the nano reactors in the thermal hydrolysis method (RM-TH) were used, and their effects on the shape, crystal structure, and size of the TiO 2 particles produced were investigated. In the RM-TH method, reverse micelles prepared by Triton X-100 / Cyclohexane / Aqueous TiCl 4 solution was used as a template since the hydrolysis reaction took place in the aqueous core of the reverse micelle that led to a controllable synthesis of TiO 2 particles. The XRD patterns of the as-prepared TiO 2 particles produced by both methods indicated that their crystal structure was rutile. In the TH method, particles were highly agglomerated resulting in a pinecone-like structure: The pinecone-like structure contained several rods with a diameter of 50 nm which were formed by conical bundles of fine rods growing radially from the center with a diameter of 6 nm and length ranged between 400 and 1000 nm. On the other hand, more uniform sphere-like nanoclusters consisting of radially growing nanorods from the center with a diameter of 6 nm and length of 200 nm were produced in the RM-TH method due to the template feature of reverse micelles. Mechanisms of nucleation and crystal growth were proposed for both production methods.
Rutile TiO 2 nanoparticles, in different structural and morphological properties, were produced by the hydrolysis of titanium tetrachloride in a highly acidic reaction media at moderate temperatures without calcination. Their photocatalytic activities were investigated in the liquid-phase degradation of terephthalic acid under visible light illumination. The parameters, which are the concentration of the titanium tetrachloride solution (0.1-1 M) and reaction temperature (60-95°C), effective on the properties of the particles, and their photocatalytic performances, were investigated. The XRD patterns indicated a pure rutile crystal structure at moderate temperatures without need of calcination. The FEGSEM images showed the formation of flower-, pinecone-, and sphere-like clusters consisting of interconnected nanofibers. The N 2 adsorption-desorption isotherms pointed out the microporous structure of the clusters. Band gap energies were found to be varying between 3.02 and 3.08 eV due to the well-developed rutile crystallite structure. Systematic studies elucidated that the optimum reactant concentration and reaction temperature are 0.5 M TiCl 4 and 95°C, respectively. The rutile clusters synthesized at the optimum reaction conditions exhibited 99 % of the photocatalytic degradation of TPA under visible light illumination at shorter irradiation times compared with commercial P25 TiO 2 .
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