Efficient N, Fe Co-Doped TiO2 Active under Cost-Effective Visible LED Light: From Powders to Films

An eco-friendly photocatalytic coating, active under a cost-effective near-visible LED system, was synthesized without any calcination step for the removal of organic pollutants. Three types of doping (Fe, N and Fe + N), with different dopant/Ti molar ratios, were investigated and compared with undoped TiO2 and the commercial P25 photocatalyst. Nano-crystalline anatase-brookite particles were successfully produced with the aqueous sol-gel process, also at a larger scale. All samples displayed a higher visible absorption and specific surface area than P25. Photoactivity of the catalyst powders was evaluated through the degradation of p-nitrophenol in water under visible light (>400 nm). As intended, all samples were more performant than P25. The N-doping, the Fe-doping and their combination promoted the activity under visible light. Films, coated on three different substrates, were then compared. Finally, the photoactivity of a film, produced from the optimal N-Fe co-doped colloid, was evaluated on the degradation of (i) p-nitrophenol under UV-A light (365 nm) and (ii) rhodamine B under LED visible light (395 nm), and compared to undoped TiO2 film. The higher enhancement is obtained under the longer wavelength (395 nm). The possibility of producing photocatalytic films without any calcination step and active under low-energy LED light constitutes a step forward for an industrial development

N, Fe single-doped and N-Fe co-doped TiO2 increasing photoactivity under visible light

Nowadays, environmental pollution is a major concern in our society and numerous researches are realized to treat water, air and soil pollution. Among the different methods developed to reduce pollution, photocatalysis is a way to degrade organic pollutants. The most widely used photocatalyst is TiO2. For several years, the sol-gel synthesis has proven effective for the synthesis of TiO2 in the form of powders or films. Aqueous and non-aqueous methods can be used to produce TiO2 by sol-gel process. Regarding the cost and the environmental impact, the aqueous way seems to be the best way to produce large amount of TiO2 materials. The aim of the present work is to develop new formulation of doped and co-doped TiO2 to extend the activity towards visible region with optimal production costs and to improve the dopant content in order to maximize the photocatalytic activity. This study presents results with catalysts powders, but the final aim is to produce doped TiO2 films as previously successfully developed

The range of validity of sorption kinetic models

Several hundred papers are published yearly reporting liquid-phase adsorption kinetics data. In general the data is analyzed using a variety of standard models such as the pseudo first- and second-order models and the Intraparticle-Diffusion model. The validity of these models is often assessed empirically via their ability to fit the data, independently of their physicochemical soundness. The aim of the present paper is to rationalize the analysis of liquid-phase adsorption kinetics data, and to investigate experimental factors that influence the adsorption kinetics, in addition to the characteristics of the adsorbent material itself. For that purpose we use a simple Langmuir adsorption–diffusion model, which enables us to identify three dimensionless numbers that characterize the working regime of any batch adsorption experiment: an adsorption Thiele modulus, a saturation modulus, and a loading modulus. The standard models are found to be particular cases of the general adsorption–diffusion model for specific values of the dimensionless numbers. This provides sound physicochemical criteria for the validity of the models. Based on our modeling, we also propose a general yet simple data analysis procedure to practically estimate the diffusion coefficient in adsorbent pellets starting from adsorption halftimes

Implications of Apparent Pseudo-Second-Order Adsorption Kinetics onto Cellulosic Materials: A Review

peer reviewedThe pseudo-second-order (PSO) kinetic model has become among the most popular ways to fit rate data for adsorption of metal ions, dyes, and other compounds from aqueous solution onto cellulose-based materials. This review first considers published evidence regarding the validity of the mechanistic assumptions underlying application of the PSO model to adsorption kinetics. A literal interpretation of the model requires an assumption that different adsorption sites on a solid substrate randomly collide with each other during a rate-limiting mechanistic step. Because of problems revealed by the literature regarding the usual assumptions associated with the PSO model, this review also considers how else to account for good fits of adsorption data to the PSO model. Studies have shown that adsorption behavior that fits the PSO model well often can be explained by diffusion-based mechanisms. Hypothetical data generated using the assumption of pseudo-first-order rate behavior has been shown to fit the PSO model very well. In light of published evidence, adsorption kinetics of cellulosic materials is expected to mainly depend on diffusion-limited processes, as affected by heterogeneous distributions of pore sizes and continual partitioning of solute species between a dissolved state and a fixed state of adsorption

TiO2 nanocrystallites photocatalysts modified with metallic species: Comparison between Cu and Pt doping

In this work, TiO2 nanoparticles were modified with different Cu and Pt species: metallic nanoparticles and ions. The photocatalysts were prepared via a sol-gel process by peptization with HNO3 at low temperature (i.e. 200 m2 g-1). The absorption property of these materials showed a visible sensitization for all samples even the pure TiO2 compared to the Evonik P25 due to N-doping confirmed by XPS analysis. The photocatalytic activity on the degradation of p-nitrophenol (PNP) showed an increase in the efficiency for nearly all catalysts compared to the pure one. Some mechanisms were proposed to explain these modifications of activity with doping. Under visible light, the photocatalysts were up to 5 times more efficient than P25 (for the best sample composed of Cu metallic nanoparticles)