1,721,153 research outputs found
Photoelectrocatalytic reactors and light sources
No full textPhotoelectrocatalysis (PEC) couples electrochemical methods with photocatalysis (PC) to enhance the separation of the photoproduced electron and hole pairs at semiconductor active surface, thus increasing the photocatalytic efficiency. PEC technology is considered one of the most promising method for processes as water treatment, fuel generation, and PEC sensing. This chapter try to link fundamental research and practical applications in photoelectrochemical engineering including reactors design strategies in different scales
Formation of high added value chemicals by photocatalytic treatment of biomass
No full textThe depletion of fossil fuel requires the search for alternative renewable feedstock and environmentally friendly methods for the production of high value-added compounds and fuels. In this context, the efficient use of biomass has emerged as a significant research field as it represents an alternative green and renewable carbon source. Various technologies have been explored for this purpose and heterogeneous photocatalysis represents a valid alternative to the catalytic methods since it can be carried out under mild experimental conditions without the addition of harmful oxidizing agents. Different biomass components have been used as the starting materials, and many valuable chemicals have been obtained with different selectivity depending on some experimental conditions as, for instance, type of photocatalyst, solvent, and physico-chemical features of the catalysts. More-over, by carrying out the reaction in de-aerated systems, in addition to high added value compounds, hydrogen can be obtained in the gaseous phase. In particular, photocatalytic conversion of lignocellulose, carbohydrates, 5-hydroxymethyl-2-furfural and glycerol (considering only the partial oxidation products) is reported
Photocatalytic ozonation for a sustainable aquaculture: A long-term test in a seawater aquarium
No full textA long-term test at a laboratory scale with a closed system (a coral reef aquarium)has been carried out to study the potentialities of photocatalytic ozonation and photocatalysis for the removal of noxious organic compounds in recirculating systems (aquaria and recirculating aquaculture systems)working with a minimum make up of new water. Attention has been focused not only on the depuration capabilities but also on possible negative phenomena, some of which could become apparent only at long times. After having tuned the system by setting appropriate operating conditions and procedures, positive results were obtained. In particular, it was observed that the alternation of photocatalytic ozonation with photocatalysis with definite cycle allowed to severely limit the presence of the organic compounds, which otherwise could accumulate in the system, and at the same time to control the formation of bromate, the ozonation side-product of main concern. In addition, the values of other parameters, which are important for water quality, remained at satisfactory values. It was also verified that the prepared photocatalytic films maintained a good photocatalytic activity even after several months of utilization in seawater. These results demonstrate that photocatalytic ozonation is a good candidate for water purification in recirculating systems in view of sustainable aquaculture
(Photo)electrocatalytic Versus Heterogeneous Photocatalytic Carbon Dioxide Reduction
Full text linkThe present review summarizes some of the main results achieved in electrochemical, photocatalytic, and (photo)-electrocatalytic systems for the reduction of carbon dioxide. After a preliminary survey of the electrocatalytic and photocatalytic systems in terms of materials used, efficiencies, operating conditions, and product distribution, it is shown how the combination of the two approaches affords often higher efficiency than the single technologies and allows better control of the product distribution. In fact, the peculiar energetic distribution at the interface of irradiated semiconductors under opportune electrical bias enables enhancement of the spatial separation of the photogenerated charges and minimization of the external energy required in electrochemical applications. Even though the efficiency of CO2 reduction is still far away from being industrially appealing, in some cases the photoelectrocatalytic systems are promising tools to be further investigated for sustainable green chemistry based CO2 utilization. The aim of this review is to examine the strengths and the weaknesses of the different approaches considering that sometimes one of the three methods can be used more successfully than the others, depending on the desired product(s) and the materials used as photocatalysts or as the (photo)electrode
Green synthesis of bromine by TiO2 heterogeneous photocatalysis and/or ozone: A kinetic study
No full textElemental bromine is an industrially relevant compound traditionally produced from bromide ions by using chlorine as the oxidizing agent. Problems related to transportation and handling of the corrosive, expensive and toxic chlorine make green synthetic alternatives highly desirable. In this paper the green synthesis of bromine from bromide in aqueous solutions under mild conditions by means of TiO2 photocatalysis and/or ozonation has been investigated from a kinetic point of view. The ozonation in the absence of the photocatalyst follows a first order kinetic with respect to both ozone and bromide. The kinetics of the reactions in the presence of the photocatalyst has been described by means of a Langmuir-Hinshelwood type model and the values of the kinetic constants and of the apparent adsorption constants have been determined. The results obtained constitute the basis for practical applications of this green and novel bromine synthesis and can be used for future reactor engineering and scale up of the process
Aqueous selective photocatalytic oxidation of salicyl alcohol by TiO2 catalysts: Influence of some physico-chemical features
Full text linkPartial photocatalytic oxidation of salicyl alcohol (2-hydroxybenzyl alcohol) to salicylaldehyde in water was investigated under environmental friendly conditions in the presence of home-prepared and commercial TiO2 (Merck and Aeroxide P25) samples under UVA irradiation. The photocatalysts were characterized by using BET, XRD, SEM and/or TEM techniques. The effects of crystallinity degree, pH (3–11) and presence of a hole trap (ethanol) on the photocatalytic activity and product selectivity were investigated. 4-Hydroxybenzyl alcohol was also used to study the influence of the position of the substituent group in the aromatic ring. High alcohols conversion and product selectivity values were obtained at pH = 11 by using well crystallized TiO2 samples. The conversion values significantly decreased by increasing the hole trap concentration, whereas the selectivity values increased slightly. The selectivity towards the corresponding aldehyde after 30% of alcohol conversion was significantly higher for 4-HBA (48%) than for 2-HBA (32%), due to the role of the para position of the substituent group. In order to clarify the different selectivity of the products, various experiments have been also performed starting from the products; these results indicate that the selectivity is also strongly dependent on the stability of the formed products under the experimental conditions used. By concluding, this article reports that the conversion and selectivity values for the studied reaction depend both on the TiO2 type and on the substrate
A dialysis photocatalytic reactor for the green production of Vanillin
Full text linkIn the present work, dialysis was used to recover vanillin while being produced by partial photocatalytic oxidation of ferulic acid in an aqueous solution at ambient temperature. The relatively high value of the permeate flux through a dense polyether-block amide membrane allowed continuously extracting vanillin from the reacting solution, thus avoiding its successive oxidation. The rate of vanillin formation was improved, compared to other reactor configurations, because intermediate compounds permeated from the reacting solution and did not hinder the reaction, while ferulic acid permeated in the opposite direction to partially replenish the reactor with the substrate. The photocatalytic membrane reactor obtained by the effective coupling of dialysis with the photocatalytic reaction improved the production yield. For instance, with the utilized experimental set up, the total amount of vanillin produced after 5 h in the membrane reactor was more than one-third higher than in the photocatalytic reactor without dialysis. The results obtained with a mathematical model agree with the experimentally observed behavior. The model allowed estimating vanillin diffusivity in the membrane and showed that concentration polarization might limit the process
Kinetic aspects of heterogeneous catalytic versus photocatalytic reactions
No full textKinetics aspects of heterogeneous catalysis and photocatalysis are reported together with the most used models developed for both fields. The chapter describes the main mechanisms involved in the different processes and the parameters used to determine their performances. A comparison of the behaviors and kinetics features of heterogeneous catalysis and photocatalysis is presented
Selective photocatalytic and photoelectrocatalytic synthesis of valuable compounds in aqueous medium
Full text linkIn the past decades, photocatalytic and photoelectrocatalytic methods have been widely employed for the degradation of harmful compounds present both is gaseous and aqueous effluents. In the last years scientists have paid great attention to the synthesis of valuable compounds and hydrogen production. Organic syntheses are generally carried out in organic solvents, under high temperature/pressure, with toxic oxidants such as permanganate. On the other hand, photocatalysis and photoelectrocatalysis using water as solvent, air or water as oxidant, and sunlight as energy source, can be an efficient alternative to the traditional, non-environmentally friendly methods. This review summarizes the photocatalytic and photoelectrocatalytic transformations of organic molecules to commercially valuable products in water, sometimes evaluating also the contemporary H2 production. The reaction conditions, mechanisms and kinetics are presented and discussed. Future perspectives are also given
Preface to the special issue entitled “New frontiers in photo(thermo)catalysis” in honour of Prof. Leonardo Palmisano
No full textThis Special issue of Catalysis Today entitled “New frontiers in photo(thermo)catalysis” is dedicated to the retirement and to the career of the colleague and friend Prof. Leonardo Palmisano who devoted his life to Science and student
- …
