1,720,995 research outputs found
Visible light driven photocatalytic hydrogen evolution using different sacrificial reagents
No full textIn this work the photocatalytic hydrogen production from aqueous solution containing organic compounds, using perovskite based photocatalyst supported on magnetic particles, was studied. In particular a photocatalyst based on Ru doped LaFeO3 was used. The photocatalyst was prepared by solution combustion synthesis using citric acid as organic fuel, and it was characterized by different techniques, such as XRD, UV-Vis DRS and Raman spectroscopy. This semiconductor has shown photocatalytic activity in presence of visible light and it was supported on Fe2O3 magnetic particles in order to remove it easily at the end of the process. The Fe2O3 particles were prepared by combustion flame synthesis, using citric acid as organic fuel and metal nitrate as iron oxide precursor. The Ru-LaFeO3 photocatalyst was coupled with magnetic Fe2O3 particles by a physical mixture in order to ensure a tight contact between the two solid phases (Ru-LaFeO3/Fe2O3). Photocatalytic tests were carried out in a pyrex cylindrical reactor equipped with a N2 distributor device and irradiated by visible-LEDs. Different aqueous solution containing organic compounds such as ethanol, glycerol or methanol were tested. The experimental results evidenced that the higher hydrogen production (about 10000 μmol L-1 after 4 h of irradiation time) was obtained in presence of methanol. The magnetic composite showed a very high stability also after several reuse cycles
Synthesis and Application of Innovative and Environmentally Friendly Photocatalysts: A Review
No full textModern society faces two major challenges: removing pollutants from water and producing energy from renewable sources. To do this, science proposes innovative, low-cost, and environmentally friendly methods. The heterogeneous photocatalysis process fits perfectly in this scenario. In fact, with photocatalysis, it is possible both to mineralize contaminants that are not easily biodegradable and to produce hydrogen from the water splitting reaction or from the conversion of organic substances present in water. However, the main challenge in the field of heterogeneous photocatalysis is to produce low-cost and efficient photocatalysts active under visible light or sunlight. The objective of this review is to compare the new proposals for the synthesis of innovative photocatalysts that reflect the requirements of green chemistry, applied both in the removal of organic contaminants and in hydrogen production. From this comparison, we want to bring out the strengths and weaknesses of the proposals in the literature, but above all, new ideas to improve the efficiency of heterogeneous photocatalysis guaranteeing the principles of environmental and economic sustainability
Catalytic non-thermal plasma reactor operating at low applied voltage for the removal of toluene in air
No full textVolatile organic compounds (VOC) represent a large group of pollutants characterized by high volatility. They can cause problems both for humans and the environment. This work aimed to examine the non-thermal plasma (NTP) technology combined with a heterogeneous catalyst ("in plasma catalysis", IPC) for the removal of toluene from the air at an applied voltage lower than that commonly reported in the literature. The NTP system was studied in the absence and presence of two commercial catalysts (gamma-Al2O3 spheres and TiO2 pellets) investigating the influence of the operating conditions (inlet flow rate, inlet pollutant concentration, water vapor presence and applied voltage). The results demonstrated that NTP without catalyst can remove toluene at voltages not less than 13.20 kV. On the other hand, the use gamma-Al2O3 in IPC configuration allowed to achieve better performance than TiO2 with the lowest applied voltage (10.67 kV) for plasma generation. Specifically, with an air flow rate of 15 NL/h at 8.7% of relative humidity and containing 500 ppm of toluene, a pollutant conversion of about 89% and a CO2/CO molar ratio equal to 4.72 was achieved. Moreover, contrary to what was observed in the NTP system without catalyst, the presence of both gamma-Al2O3 and TiO2 in the IPC configuration allowed to avoid the presence of O-3 and NOx at the reactor outlet. Finally, the calculated energy efficiency was in the order NTP+ gamma-Al2O3 > NTP+TiO2 > NTP alone
Cu-doped ZnO as efficient photocatalyst for the oxidation of arsenite to arsenate under visible light
Full text linkIn this work, photocatalytic oxidation of As(III) to As(V) by ZnO photocatalyts doped with Cu was investigated under visible light. Photocatalysts were successfully prepared by precipitation method. The obtained samples were characterized by N2adsorption at −196 C, X-Ray fluorescence analysis, X-ray diffraction, Raman spectroscopy, scanning electron microscopy and UV–vis reflectance analysis. In particular, according to XRD analysis, all samples showed an hexagonal wurtzite structure with average crystallite sizes approximately in the range 32–33 nm. The doping with Cu allowed to obtain a decrease of band gap energy from 3.2 eV, typical of pure ZnO, to 2.92 eV. Photocatalytic oxidation tests under visible light showed that undoped ZnO is not able to oxidize the As(III) present in solution, while the complete conversion of As(III) to As(V) was achieved in the presence of Cu doped ZnO photocatalyst. The best photocatalytic activity was observed with ZnO doped with 1.08 mol% of Cu (1.08Cu_ZnO), within 120 min of exposure to visible light irradiation. The same result was observed under solar simulated radiation. Photocatalytic tests were carried out also in real drinking water and complete oxidation of As(III) to As(V) by 1.08Cu_ZnO photocatalyst was achieved in 120 min under both visible light (emitted by LEDs) and solar simulated radiation
Enhanced Photocatalytic Hydrogen Production from Glucose Aqueous Solution Using Nickel Supported on LaFeO3
No full textNowadays one of the topics of greatest interest to the scientific community is the search for new eco-friendly technologies that allow the production of energy. In particular, one of the main players in this area is hydrogen. Several innovative processes are proposed in the literature for the production of hydrogen. One of these is the heterogeneous photocatalysis. Furthermore, it is also interesting to evaluate the source from which hydrogen is obtained. An interesting solution is glucose, one of the most familiar biomass, which can be used to produce hydrogen from a photocatalytic process. For this reason, in this work we propose the use of Ni as active phase supported on LaFeO3 photocatalyst for the renewable H2 production from glucose aqueous solution. Perovskite photocatalysts are quite encouraging materials for H2 production from aqueous solution owing to their stability in water. Low-cost nickel can be used to improve the performance of perovskites, modifing their surface and thus avoiding the use of expensive noble metal based cocatalysts. Specifically, the LaFeO3 catalyst was prepared by solution combustion synthesis using citric acid as organic fuel. A specific amount of Ni was deposited on LaFeO3 surface by chemical reduction method, using sodium borohydride (NaBH4) as a reducing agent. The prepared samples were characterized by different techniques, such as XRD and UV-Vis. The photocatalytic tests were carried out in a pyrex cylindrical reactor equipped with a N2 distributor device and irradiated by four UV lamps (emitting at 365 nm) positioned at the same distance from the external surface of the reactor (about 30 mm). The tests were realized with a solution volume equal to 80 ml, an initial concentration of glucose equal to 5550 umol L-1 and a catalyst dosage equal to 1.5 g L-1. The experimental results evidenced that the presence of Ni on LaFeO3 surface enhanced the H2 production and in particular the highest hydrogen production (about 2242 umol L-1 after 4 h of irradiation time) was obtained with Ni/LaFeO3, whereas the raw LaFeO3 was able to produce a lower H2 amount (about 1394 umol L-1 after the same irradiation time)
Highly-efficient hydrogen production through the electrification of OB-SiC nickel structured catalyst: Methane steam reforming and ammonia cracking as case studies
No full textThe aim of this work is the preparation and the electrification of Ni_CeO2_Al2O3/OBSiC (Oxygen Bonded SIlicon Carbide) based foams used in two different endothermic reactions for H2 production: methane steam reforming and ammonia cracking. In particular, the heating of the catalytic foams occurs by the Joule effect, and to guarantee a uniform temperature profile in both the axial and radial direction, two different heating resistances were used. In addition, the high tortuosity together with the very high thermal conductivity of the OBSIC carrier, allow to overcome the heat and mass transfer limitations achieving a better control of the reaction behavior. Wet impregnation method was adopted for the Ni and Ce deposition, while the final catalysts was characterized through Hg penetration technique, Scanning Electron Microscope (SEM), N2 adsorption @77 K for the specific surface areas (SSA) determination and X-ray diffraction (XRD). The methane steam reforming and ammonia cracking tests were both carried out, in the same reactor, but at different space velocity values (WHSV). The results obtained are exciting, not only in terms of equilibrium approach and hydrogen production, but also in terms of energy consumption as kWh/Nm3 of H2 produced. In particular, in the case of methane steam reforming the results showed an energy consumption E [kWh/Nm3 H2] equal to 1.21 obtained at WHSV equal to 6.2 h−1, very close to the theoretical limit of 0.98 kW h/Nm3 H2. Also, for ammonia cracking, the energy consumption was very promising considering the scale of our reactor, with 1.5 kW h/Nm3 H2 obtained at a WHSV of 2.27 h−1, considering the theoretical limit equal to 0.71 kW h/Nm3 H2
Enhanced azo dye removal in aqueous solution by H2O2 assisted non-thermal plasma technology
No full textThe focus of the present study is to assess the performances of H2O2 assisted non-thermal plasma (NTP) technology for the degradation of the Acid Orange 7 textile azo dye in aqueous solution. The reactor configuration used during the experiments was the “dielectric barrier discharge” (DBD). The comparison between DBD (only non-thermal plasma) and H2O2/DBD system (in the presence of H2O2 in the solution) was also performed. The experimental tests were carried out using 100 mL of aqueous solution with an initial Acid Orange 7 concentration equal to 10 mg/L, in the presence of oxygen as process gas in the DBD reactor operating with 20 kV of applied voltage. The results demonstrated that in presence of only oxygen in the DBD reactor, a discoloration and simultaneous mineralization of about 60% was obtained after only 2.5 min, while the addition of H2O2 enhanced the dye degradation rate, obtaining in the same a discoloration and simultaneous mineralization of about 80%. The higher degradation rate achieved by adding H2O2 could be attributed to the presence of higher amounts of hydroxyl radicals in DBD reactor. A deeply study on the influence of the main macroscopic parameters such as O2 flow rate, H2O2 and Acid Orange 7 initial concentration has been assessed in order to find the optimal operating conditions for the H2O2/DBD system. The kinetic evaluation and the energy yield study were performed under specific experimental condition. If compared with traditional AOPs, the results obtained with the H2O2/DBD system, showed that this technology is faster and extremely efficient and consequently very promising for the removal of Acid Orange 7 azo dye in aqueous solutions
Photocatalytic hydrogen production from glycerol aqueous solution using Cu-doped ZnO under visible light irradiation
No full textCu-doped ZnO photocatalysts at different Cu loadings were prepared by a precipitation method. The presence of Cu in the ZnO crystal lattice led to significant enhancement in photocatalytic activity for H2 production from an aqueous glycerol solution under visible light irradiation. The best Cu loading was found to be 1.08 mol %, which allowed achieving hydrogen production equal to 2600 μmol/L with an aqueous glycerol solution at 5 wt % initial concentration, the photocatalyst dosage equal to 1.5 g/L, and at the spontaneous pH of the solution (pH = 6). The hydrogen production rate was increased to about 4770 μmol/L by increasing the initial glycerol concentration up to 10 wt %. The obtained results evidenced that the optimized Cu-doped ZnO could be considered a suitable visible-light-active photocatalyst to be used in photocatalytic hydrogen production without the presence of noble metals in sample formulation
Non-thermal plasma-assisted catalytic reactions for environmental protection
No full text“Non-thermal plasma technology” (NTP) has notably increased [...
Photocatalytic removal of methyl orange azo dye with simultaneous hydrogen production using ru-modified zno photocatalyst
No full textThe aim of this work is to demonstrate the effectiveness of the photocatalytic process in the Methyl Orange azo dye degradation and simultaneous H2 production by using ZnO doped with ruthenium. Ru-modified ZnO photocatalysts were prepared by precipitation method and were characterized by different techniques (XRF, Raman, XRD, N2 adsorption at −196 °C, and UV–vis DRS). The experiments were carried out in a pyrex cylindrical reactor equipped with a nitrogen distributor device and irradiated by four UV lamps with the main wavelength emission at 365 nm. Different Ru amounts (from 0.10 to 0.50 mol%) were tested in order to establish the optimal amount of the metal to be used for the ZnO doping. The photocatalytic activity was evaluated both in terms of Methyl Orange removal and hydrogen production. The experimental results showed that the best activity, both in terms of H2 production and Methyl Orange degradation, was obtained with the Ru-modified ZnO photocatalyst at 0.25 mol% Ru loading. In particular, after four hours of UV irradiation time, the discoloration and mineralization degree were equal to 83% and 78%, with a simultaneous hydrogen production of 1216 μmol L−1. This result demonstrates the ability of the photocatalytic process to valorize a dye present in wastewater, managing to obtain a hydrogen production comparable with the data present in the literature today in the presence of other sacrificial substances
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