1,720,968 research outputs found
Solar-powered photocatalysis in water purification: applications and commercialization challenges
Full text linkAlthough heterogeneous photocatalysis has been recognized as a promising technology for decontaminating and disinfecting municipal and industrial wastewater over the last few decades, it has not yet successfully transitioned from laboratory-scale research to real-world applications. This limited progress is attributed to inherent physicochemical properties of most photocatalytic materials available, which exhibit reduced photoefficiency under visible light irradiation, along with multiple engineering considerations. This comprehensive review delves into the intricate dynamics of photocatalytic reactions kinetics, exploring several types of photocatalytic reactors and elucidating the significance of materials employed in photocatalytic wastewater treatment. This critical survey systematically examines the effectiveness of different materials such as titania, zinc oxide and graphitic carbon nitride which are commercially applied for different reactor systems. Understanding the role of these materials for photocatalytic reactions is essential to address the challenges associated with wastewater treatment. Furthermore, the discussion extends beyond the technical aspects to encompass the broader landscape of challenges hindering the commercialization and widespread adoption of photocatalytic technologies. By critically evaluating these challenges, the minireview aims to provide valuable insights for researchers, engineers, and policymakers seeking to advance and implement photocatalytic wastewater treatment on a broader scale. This synthesis of knowledge consolidates the current state of the field and outlines future prospects for overcoming barriers and optimizing the potential of photocatalytic processes in environmental remediation
Implementing a sustainable process for the recovery of palladium from spent catalysts at industrial scale: A LCA approach
Full text linkDue to its unique physicochemical properties, palladium is widely used in several industry applications (e.g., vehicle emission control). In view of the circular economy, it is essential to explore secondary sources of palladium, such as urban mines. Current technologies for effective palladium recovery involve high energy consumption and severe environmental impact. More recently, a novel green method for recovering palladium from spent catalysts through a combination of mild acidic leaching and photodeposition on ZnO nanoparticles was proposed on a laboratory scale. In the present study, the environmental impacts of this recovery method, properly upscaled and modelled, was assessed by employing the LCA approach. Specifically, a comparative LCA was carried out for the process with as well as without recycling key components, such as Cu (II) and NaCl for the leaching solution and ZnO. The outcomes identified critical areas and drove the investigation of alternative process configurations to reduce its environmental footprint, such as the use of carbon dioxide in the photodeposition process with the aim of decreasing the resulting terrestrial ecotoxicity. This study marks a significant step forward in advancing research toward industrial−scale implementation of palladium recovery. It provides valuable insights for researchers in the field of green physicochemical processes for metal recovery, thus offering guidance for future decision−making towards more sustainable practices
Enhanced photocatalytic hydrogen evolution via ball-milled PtO<sub>2</sub>/TiO<sub>2</sub> heterojunction photocatalyst: an alternative approach for efficient energy production
No full textA novel PtO2/TiO2 heterojunction photocatalyst was synthesized via ball milling and investigated for its potential in photocatalytic hydrogen production. The effects of PtO2 loading, catalyst concentration, and sacrificial agent concentration on the hydrogen evolution rate (HER) were systematically evaluated. The results indicate that increasing the PtO2 concentration in the catalyst significantly enhances the hydrogen production rate, reaching a maximum value of approximately 54 mmol∙h−1∙g−1 at a PtO2 concentration of 20 wt%. The effect of the sacrificial agent concentration on the hydrogen production exhibited a Langmuir-Hinshelwood behavior with constant hydrogen production rates at sacrificial agent concentrations greater than 2.5 M. The experimental results were described by a kinetic model to shed light on the reforming mechanism. Finally, the stability of the photocatalyst was confirmed through four consecutive cycle tests. This synergistic integration of experimental and modelling analyses provides a robust platform for uncovering mechanistic details of photocatalytic hydrogen generation using a photocatalyst synthesized through a facile preparation method.</p
UV‐Solar Photocatalysis for the Simultaneous Removal of Arsenic and Mercury in Washing Solutions from Polluted Marine Sediments
Full text linkAn environmentally sustainable strategy has been developed for simultaneously removing arsenic and mercury from wastewater, potentially coming from washing of polluted marine sediments. Citric acid (CA), a biodegradable chelating agent, forms stable complexes with both metals, which can be extracted from contaminated sediments through ex situ sediment washing. A solar photocatalytic method has been developed to separate toxic metals from wastewater and degrade CA. Increasing the TiO2 photocatalyst load enhances arsenic adsorption under dark conditions. Total arsenic removal is achieved during photocatalytic decontamination using 1000 ppm of TiO2. Fe(III)–hydroxides formed in the presence of Fe(III) further adsorb arsenic. Nearly total arsenic removal is achieved even under seawater conditions and visible light irradiation only. The removal of arsenic in different oxidation states has been successfully demonstrated. The UV–vis/TiO2/CA photocatalytic system has also proven highly effective for mercury removal from wastewater. Although seawater conditions slightly slow the removal process, complete mercury removal is achieved even under visible light irradiation. Finally, a combined photocatalytic approach has been developed for the removal of both arsenic and mercury, achieving 100% removal within few minutes of light irradiation. The reaction mechanism has been depicted based on intermediates and reaction products detected during the photocatalytic process
Hydrogen production through photoreforming processes over Cu2O/TiO2 composite materials: A mini-review
Full text linkCu2O 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
Hydrogen production upon UV-light irradiation of Cu/TiO2 photocatalyst in the presence of alkanol-amines
No full textPhotoactivated Fe(III)/Fe(II)/WO3–Pd fuel cell for electricity generation using synthetic and real effluents under visible light
No full textSolar 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
A novel green approach for silver recovery from chloride leaching solutions through photodeposition on zinc oxide
No full text: 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
Photocatalytic hydrogen production through photoreforming of organics using copper – based photocatalyst under visible light radiation
Full text linkNowadays, 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
Unravelling the photoactivity of metal-loaded TiO2 for hydrogen production: Insights from a combined experimental and computational analysis
Full text linkDespite being the most employed material for photocatalytic hydrogen generation, TiO2 suffers limitations such as a high rate of electron-hole recombination and poor light absorption in the visible spectrum. Among the various strategies developed to overcome these drawbacks, combining TiO2 with a metal co-catalyst emerged as one of the most promising. In this study, we integrated experimental findings, advanced characterization techniques, and computational methods to shed light on how different noble metals influence the enhancement of the photocatalytic activity of TiO2. Among the tested noble metal co-catalysts, the hydrogen production rate under UV and visible light irradiation followed the trend Pt > Au ≈ Pd > Ag > bare TiO2, with Pt-decorated TiO2 exhibiting a hydrogen production rate of 28 mmol/h g. The noble metals were found to significantly suppress the electron-hole recombination rate compared to bare TiO2. Upon photodeposition, Pd and Pt formed the smallest nanoparticles with average sizes of 13.4 nm and 4.1 nm, respectively. Computational analyses were conducted to rationalize the difference in nanoparticle sizes by analyzing the binding and cohesive energies of the metal clusters on the TiO2 surface. Additionally, calculations demonstrated the strong interaction of Pt, Au, and Pd nanoclusters with adsorbed hydrogen, with Pt achieving the closest-to-zero Gibbs free energy of hydrogen adsorption and displaying the most polar interaction with hydrogen. These findings align closely with the observed hydrogen production rates, where UV/Vis-driven hydrogen production is governed by the coupling of hydrogen radicals on the co-catalyst surface, while visible-light-driven production is limited by charge carrier lifetimes
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