New insights into the efficient charge transfer of ternary chalcogenides composites of TiO2

Abstract A two-step solvothermal synthesis was adopted to prepare AgXSe2-TiO2 (X = In, Bi) composites. DFT study of the pristine parent samples showed the formation of the hexagonal phase of AgBiSe2, and tetragonal phase of AgInSe2 and TiO2, which corroborated the experimentally synthesised structures. Both the AgBiSe2-TiO2 and AgInSe2-TiO2 composites displayed enhanced visible light absorption and reduced band gap in the UV-DRS patterns. The XPS results exhibited a shift in binding energy values and the TEM results showed the formation of spherical nanoparticles of both AgBiSe2 and AgInSe2. The PL signals displayed delayed recombination of the photogenerated excitons. The as synthesised materials were studied for their photocatalytic efficiency, by hydrogen generation, degradation of doxycycline, and antimicrobial disinfection (E. coli and S. aureus). The composite samples illustrated more than 95 % degradation results within 180 min and showed 5 log reductions of bacterial strains within 30 min of light irradiation. The hydrogen production outcomes were significantly improved as the AgBiSe2 and AgInSe2 based composites illustrated 180-fold and 250-fold enhanced output compared to their parent samples. The enhanced photocatalytic efficiency displayed is attributed to the delayed charge recombination of the photogenerated electron-hole pairs in the AgXSe2-TiO2 interface. Formation of a p-n nano heterojunction for AgBiSe2-TiO2 and type II heterojunction for AgInSe2-TiO2 composite are explained

Photocatalytic hydrogen production through photoreforming of organics using copper – based photocatalyst under visible light radiation

Nowadays, 80% of global energy consumption is dependent on fossil fuels, leading different problems such as the decreasing of energy sources and the environmental problems (global warming, greenhouse effect, production of harmful gases, ozone layer depletion and acid rain). Hydrogen represents a potential alternative energy carrier due to its stability and zero emission of greenhouse gases, and many researches are directed toward the utilization of metal oxides semiconductors (such as TiO2 and ZnO) as photocatalysts to convert solar energy into hydrogen; in particular TiO2, due to its high chemical stability and photocatalytic activity in the UV range is the most widely used material; despite the great number of positive characteristics, TiO2 presents different problems such as high electron – hole recombination rate and poor absorption under the visible light, due to its wide band gap (about 3.2 eV). To overcome these drawbacks, several studies reported the utilization of TiO2 in association with other semiconductors such as ZnO and Cu2O; in particular much attention has attracted Cu2O: this is a non-toxic and abundant material, with a narrow band gap (about 2.1 eV); as p – type semiconductor, if combined with a n – type semiconductor, it is able to form a heterojunction photocatalyst, extending the light absorption in the visible range and reducing of electron-hole recombination rate. Several techniques have been used for Cu2O/TiO2 composite preparation and numerous disadvantages are still associated to each of them. In the present research, based on the outcomes of an extended literature analysis, a ball milling method to dryness has been chosen as alternative technique to prepare the photocatalysts, due to its simplicity and industrial applicability. The effect of milling time, rotation rate and Cu2O percentage on the photocatalytic hydrogen generation have been evaluated, obtaining the best performances (H2 generation about 60 μmol/h) with a milling time of 1 minute and a rotation rate of 200 rpm, when 1%wt of Cu2O is used in the composite in presence of methanol as scavenger. Moreover, the effect of the sacrificial agent used is evaluated adopting in the tests other species, and recognizing glycerol as the best candidate to produce hydrogen among the tested organics. Furthermore, the photocatalytic activity of the best prepared photocatalyst was evaluated at varying the pH and the temperature of the suspension, methanol concentration and catalyst load. In particular, a great positive effect was recorded at increasing the temperature of the system, showing a hydrogen productivity about 4.5 – fold higher than that obtained at the lowest temperature. Moreover, being the aim of the present work devoted to the development of a visible light active photocatalytic system, the possibility of using it by exploiting the solar light was evaluated, obtaining a hydrogen production about 5 – fold higher than that collected under simulated solar conditions. Finally, the development of a suitable mathematical model able to predict the hydrogen production in presence of the selected catalyst was also attempted

Photocatalytic Applications in Wastewater and Air Treatment: A Patent Review (2010–2020)

In this work, we reviewed the most significant patents of the last decade (2010–2020) in the fields of water and air photocatalytic treatment. Patents were discussed by identifying the recurrent addressed issues and presenting the proposed solutions. Adoption of TiO2 and/or modified-TiO2-based material is still the most common choice of inventors, whereas many patents focus on the design of the plants/devices to improve efficiency of photocatalytic treatment by improving light utilization and contact between the phases. The review also highlights issues deriving from specific applications and outlines future trends in the field, such as the need for standardized testing and digitalization of monitoring and control

Hydrogen production through photoreforming processes over Cu2O/TiO2 composite materials: A mini-review

Cu2O is a promising low-cost semiconductor exhibiting a narrow band gap. The combination of p-type Cu2O with n-type TiO2 results in a p-n heterojunction highly beneficial to photocatalytic processes, due to the resulting capability of (i) absorbing visible light irradiation and (ii) promoting charge carrier separation. An intense scientific activity has been recorded in the field of H2 generation through water photosplitting and organic photoreforming over Cu2O/TiO2-based composites. This literature survey aims at clarifying conflicting information on the preparation, characterization, and use of Cu2O/TiO2 composites for H2 evolution. Detailed information on analytical techniques devoted to uniquely identifying Cu2O has been provided. Preparation method, effect of pH, effect of sacrificial agent, chemical stability of Cu2O/TiO2 composites, and reaction mechanisms have been critically discussed. The highest efficiency values obtained over Cu2O/TiO2 photocatalysts have been reported. A solid groundwork on which developing new effective and low-cost materials for H2 generation has been provided

Visible—Light Driven Systems: Effect of the Parameters Affecting Hydrogen Production through Photoreforming of Organics in Presence of Cu₂O/TiO₂ Nanocomposite Photocatalyst

Several studies have shown that combining TiO2 and Cu2O enhances the photocatalytic activity of the material by generating a heterojunction capable of extending the light absorption in the visible and reducing the electron-hole recombination rate. Ball milling has been chosen as an alternative methodology for photocatalyst preparation, among the several techniques documented in the literature review. The results of a previously reported investigation enabled the identification of the most effective photocatalyst that can be prepared for hydrogen generation by combining Cu2O and TiO2 (i.e., 1%wt. Cu2O in TiO2 photocatalyst prepared by ball-milling method at 200 rpm and 1 min milling time). To optimize photocatalytic hydrogen generation in the presence of the greatest photocatalyst, the effects of (i) sacrificial species and their concentration, (ii) temperature, and (iii) pH of the system are taken into account, resulting in a light-to-chemical energy efficiency of 8% under the best-tested conditions. Last but not least, the possibility of using the present photocatalytic system under direct solar light irradiation is evaluated: the results indicate that nearly 60% of the hydrogen production recorded under sunlight can be attributed to the visible component of the solar spectrum, while the remaining 40% can be attributed to the UV component

A novel green approach for silver recovery from chloride leaching solutions through photodeposition on zinc oxide

: Silver is extensively used in electronics, industrial catalysis, and biomedical sector owing to its enhanced physicochemical properties. E-waste recycling may contribute significantly to enhance silver recovery in the view of a circular economy and limit the depletion of mineral sources. In this scenario, hydrometallurgical routes represent the most widely used techniques for silver extraction/recovery and require strong acidic solutions, high temperatures, and multiple operating units. An alternative sustainable route for silver recovery from leaching solutions used for silver extraction in industrial applications is herein proposed for the first time. The novel green process of silver recovery is based on the UV/vis light-driven photocatalytic deposition of pure metallic silver over low-cost and non-toxic ZnO photocatalyst. In the second step, ZnO is dissolved by slight acidification and pure metallic silver is easily recovered. Low environmental impact, mild operating conditions, and economic viability are among the major perks of the new silver recovery process developed. In the view of a full-scale implementation, several operating conditions of the recovery process (i.e., photocatalyst load, starting silver concentration, type of hole scavenger and irradiation) were thoroughly investigated. A mathematical model capable of describing the system behaviour under different operating conditions was also developed and allowed to estimate unknown kinetic parameters for the Ag-photodeposition process

Photoactivated Fe(III)/Fe(II)/WO3–Pd fuel cell for electricity generation using synthetic and real effluents under visible light

Solar energy exploitation is one of the most challenging applications for sustainable energy production. In this work a photoactivated fuel cell was developed, using visible light and the Fe(III)/Fe(II) redox couple for the simultaneous production of electrical energy and oxidation of polluting organics (alcohols) contained in synthetic and real wastewaters. WO3 was selected as a cheap and environmentally friendly photocatalyst more efficient than TiO2 (i) under visible light irradiation and (ii) in the presence of in-situ photodeposited Pd. Pd photodeposition was found to reduce the band gap of bare WO3, thus increasing visible light capture and limiting the occurrence of photogenerated hole/electron recombination. Higher photocatalytic performances were recorded over WO3–Pd compared to TiO2 and bare WO3, despite the low BET superficial area of WO3–Pd (2.34 m2 g−1). Optimal conditions were identified at pH = 2.0 with 2% w/w Pd load. The results also evidenced the influence of the selected sacrificial organics and water matrices. A quantum yield of 84.89% and an energy efficiency of 4.15% were the best results achieved so far for the proposed system. The present photoelectrochemical cell offers a very promising system for electrical energy production by using wastewater from wine manufacturing industry and solar light radiation