太阳能光催化染料污水脱色研究

以太阳光中近紫外光激发催化剂ＴｉＯ２将染料污水光催化脱色，探讨催化剂用量，催化剂活性、曝气、污水流速、光催化反应器受辐射面积、太阳辐照度等条件对染料污水脱色效率的影响。结果表明，在一般晴天经２ｈ的太阳光照射，阳离子蓝Ｘ－ＧＲＲＬ的脱色效率在８０－９３％之间，即使在阴天多云条件下，脱色效率亦可达到６６％，表明太阳能光催化染料污水脱色处理是一种经济、实用、高效的污水脱色处理技术。     

Solar photoreactors comparison based on oxalic acid photocatalytic degradation

Solar heterogeneous photocatalytic degradation of oxalic acid in water is carried out in four different solar photoreactors: a parabolic trough concentrator (PC), a tubular collector (TC), a compound parabolic collector (CPC), and a V-trough collector (VC). The reactors operate under equal conditions of solar irradiance, collection surface and fluid flow rate to ensure a better comparison between the systems. The effects of TiO₂ catalyst concentration and radiation incidence angle on the degradation are studied. Oxalic acid degrades without appreciable generation of intermediates, and a simple kinetic model is proposed to describe the process. There are differences in the degradation rates depending on the collector geometry. The CPC shows the best overall performance in terms of accumulated energy, followed closely by the VC. Incidence angle affects the total amount of energy collected but does not reduce very much the efficiency of the reactors to use this energy in the photocatalytic process.     

Photocatalytic water treatment: solar energy applications

During the past 20 years research and development in the area of photocatalysis have been tremendous. One of the major applications of this technology is the degradation of organic pollutants in water and air streams which is considered as one of the so-called advanced oxidation processes. This overview briefly describes the basic principles of photocatalysis, focusing in particular on important mechanistic and kinetic aspects as well as on some requirements for efficient photocatalysts. Since the comparatively high costs associated with the generation of light from electricity constitute one of the major drawbacks particularly for the rapid commercialization of photocatalytic water treatment units, solar photons have been utilized here with great success for many years now. Various solar reactors for the photocatalytic water treatment are described in detail in the main part of this review including the comparison of their overall performance.     

Photocatalytic degradation of organic dyes under UV–Visible light using capped ZnS nanoparticles

Purification techniques like ozonization, chlorination and filtration have their own limitations of corresponding energy sources and harmful waste generation. However, heterogeneous photo catalysis is used for producing oxidative agent (hydroxyl radical) which has been used as an environmentally harmonious decontamination process. Such safe and low energy consumable photo catalytic system is required for purification of polluted water. Degradation of dyes is a standard method to check the photocatalytic activity of any type of photo catalyst. In this paper thioglycerol capped and uncapped ZnS nanoparticles are studied in detail for their photocatalytic activity and generation of electron hole pairs. Bromophenol blue, crystal violet and reactive red dyes were successfully photo reduced using ZnS nanoparticles after 3.0 h of irradiation. Since the photocatalytic activity depends on the generation of electron hole pairs and the existence of different phases, we have tried to correlate the optical and morphological studies with these results to understand the phenomenon of photocatalytic activity at nanoscale. Though the Ultra violet irradiation can efficiently degrade the dyes, naturally abundant solar radiation is also very effective in the mineralization of dyes. Hence, it may be a viable technique for the safe disposal of textile wastewater into the water streams.     

Nanostructured materials for the visible-light driven hydrogen evolution by water splitting: A review

The conversion of abundantly available photonic energy into useful chemical energy is considered to be a greener protocol for addressing the energy shortage. Recently, since most of the emphasis has been centralized on the semiconductor-based photocatalysis; the designing and fabrication of the novel semiconductor photocatalytic material is happening at a blistering rate. Recently, the nanostructured materials have attracted ever-growing research attention as photocatalytic material for hydrogen generation reaction by dissociation of water. Such photocatalytic nanomaterials are known to exhibit superior activity than their corresponding bulk counter-parts because of the improved interfacial charge separation and the broad surface area providing sufficient active sites. However, the improvement in the efficiency and selectivity towards hydrogen production reaction under solar or visible light radiation always remains a challenging assignment. In the present review, the segregation of the so far reported nanostructured photocatalysts into different categories, based on their dimensionality such as 0-D, 1-D and 2-D materials, is implemented. Furthermore, their synthetic route and the photocatalytic hydrogen evolving efficiencies are explored and briefly summarized. Moreover, the methodology of development of nanocomposite materials leading to the construction of heterojunctions including Type-I, Type-II, Type-III, Z-Scheme and S-Scheme system is also discussed. In addition, an in-depth investigation on the charge carrier's generation, separation and their transportation is also reviewed. Finally, the future perspectives regarding the designing of an efficient, stable and economic photoactive nano-architecture material for the efficient hydrogen production via photocatalytic dissociation of water are also pointed.     

Photocatalytic reaction of 2-propanol over WO3/SiO2 using high flux radiation

The decomposition of 2-propanol is used as a model to investigate the photocatalytic properties of tungsten (VI) oxide on silica gel. A high flux, simulated solar radiation source is utilized as the energy source for the reactions. The UV-visible photocatalytic activity decreases with an increase in percent of WO₃ loading on SiO₂ from 1% to 3%. IR radiation, carrier gas, and the lamp power also play an important role in this reaction. The IR and the higher lamp power tend to enhance thermal reaction by heating the surface of the catalyst. In contrast to helium, use of argon carrier gas also enhances thermal reaction. Presumably the catalyst surface temperature is greater in the presence of argon due to the lower gaseous thermal conductivity of argon. UV-visible photocatalytic activity is most obvious when a water filter is used to remove the IR radiation and helium is used as the carrier gas. This study also supports a procedure established earlier to evaluate photochemical reactions, including photocatalysis.     

Green fabrication of graphene quantum dots from cotton with CaSiO3 nanostructure and enhanced photocatalytic performance for water treatment

Perovskite nanostructures have become one of the most alluring classes of materials because of their structure and properties, which have revolutionized many areas of electronics, optoelectronics, and photonics. In this research, CaSiO₃ nanostructures have been prepared by hydrothermal synthesis as profitable and light-active materials for photocatalytic activities. The photocatalytic procedure is an eco-friendly method, which is recognized as an effective alternative for the degradation of multiple hazardous materials. In this regard, photocatalytic properties of oxide perovskite have been developed by effective incorporation of CaSiO₃ nanostructures with graphene quantum dots (GQDs) under facile green low-cost hydrothermal conditions. The impact of two factors, including diverse varieties of surfactants and concentration of GQDs, was surveyed through XRD, FESEM images, and diffuse reflectance spectroscopy (DRS) on purity, structure, and photocatalytic performance. The results demonstrated that the CaSiO₃/GQDs in high-level concentration showed higher visible-light photocatalytic activity. Besides, the kinetics of photocatalytic reactions was investigated, and the outcomes showed that higher photocatalytic performance possessed a higher reaction rate coefficient.     

Construction of photocatalytic plates for hydrogen production from photoreforming of glycerol

The photocatalytic production of hydrogen has been reported as an attractive strategy given the possibility of using renewable sources such as sunlight and biomass. The scalability of the process involves optimizing the design of the reaction system, minimizing the cost and time spent on the stages of separation, purification and reuse of the catalyst. This work demonstrates the application of photocatalytic plates impregnated with TiO₂ doped with small doses of platinum (Pt) in the photoreforming of glycerol under visible radiation. The optimized amount of catalyst was 25 mg, corresponding to an average hydrogen production rate in 3 h of reaction of 316 mmol H₂.h⁻¹.m⁻², this value being independent of the platinum concentration range tested (0.1%–1.0%, w/w). The kinetic behavior of the photocatalytic plates was similar to the application of the catalyst in powder form. The presence of 0.3% platinum in the catalyst composition led to the maintenance of photocatalytic stability for 7 consecutive application cycles, indicating operational viability without appreciable loss of performance, brings good prospects for expanding the scale of the process and allowing the development of continuous flow operations.     

Stacked nano rods of cobalt and nickel based metal organic frame work of 2–amino benzene dicarboxylic acid for photocatalytic hydrogen generation

Stacked nanorods of cobalt and nickel based hetero bimetallic organic frameworks (MOFs) of 2–amino benzene dicarboxylic acid are developed as photocatalyst for hydrogen evolution reaction. The ratio of metals in the catalyst is tuned to achieve a narrow band gap, and the MOF with optimized Ni to Co ratio of 1: 0.5 (1Ni0.5Co@NH₂BDC) exhibited the lowest band gap (2.2 eV) and electron–hole recombination rate. The catalyst exhibits enhanced photocatalytic activity for hydrogen evolution reaction due to the absorption of photons by 2–amino benzene dicarboxylic acid and excitation of electrons from HOMO to LUMO of the organic linker. The excited electrons relay to the cluster of the framework and reduce the protons gather around the cluster to hydrogen. The holes in the HOMO state are occupied by the electrons from the sacrificial agents and it supports the photocatalytic hydrogen evolution by avoiding electron–hole recombination. The stability of MOF catalyst in water splitting medium even with sacrificial agents confirms its competency with the state–of–the–art photocatalytic materials.     

New and emerging developments in solar energy

Solar energy can potentially play a very important role in providing most of the heating, cooling and electricity needs of the world. With the emergence of solar photocatalytic detoxification technology, solar energy also has the potential to solve our environmental problems. However, we do not see widespread commercial use of solar energy. Some of the emerging developments in solar may change that situation. This paper describes some of the new and emerging developments, with special emphasis on: (1) nanoscale antennas for direct conversion of sunlight to electricity with potential conversion efficiencies approaching 80–90%; (2) new thermodynamic cycles for solar thermal power, that have the potential to reduce capital costs by 50%; and (3) solar photocatalytic oxidation for cleanup of industrial wastewater, drinking water, soil and air. The paper describes the fundamentals of each of these developments, their potential, present status and future opportunities for research.(1) Nanoscale antenna solar energy conversion: The current photovoltaic technologies rely on the quantum nature of light and semiconductors which are fundamentally limited by the band-gap energies. A revolutionary new approach suggested by Professor Robert Bailey in 1972 revolves around the wave nature of light. Professor Bailey suggested that broadband rectifying antennas could be used for solar to d.c. conversion. These rectennas would not have the fundamental limitation of semiconductor band-gap limiting their conversion efficiencies. Rectennas for solar conversion would have dimensions of the order of the wavelengths of solar radiation which falls mostly in the sub-micron range. The challenges in actually achieving the objectives are many. This paper describes the challenges and approaches to their solution.(2) New thermodynamic cycles for solar thermal power: It is recognized that the capital costs of solar thermal power will have to be reduced by about 50% in the near future in order to make it competitive with fossil fuels (especially natural gas) based power systems. Potential exists for meeting this goal by reducing the costs and improving the thermodynamic performance of power cycles by hybridization and combined cycle approaches and by employing new and innovative ideas in thermal power cycles. This paper describes the new thermodynamic approaches with an emphasis on an innovative new thermodynamic cycle using ammonia and water mixtures as the working fluids.(3) Solar photocatalytic detoxification and disinfection of water and air: Although the potential of solar radiation for disinfection and environmental mitigation has been known for years, only recently has this technology been scientifically recognized and researched. Solar photocatalytic oxidation has been demonstrated to effectively treat groundwater, drinking water, and industrial wastewater. In some applications such as decoloration and reduction of COD it may be the only effective method of treatment. Treatment of indoor air by the photocatalytic method has been demonstrated as the most effective technology for that application. This paper describes the recent developments and identify challenges and future research opportunities.     

Enhanced photocatalytic H2 evolution and anti-photocorrosion of sulfide photocatalyst by improving surface reaction: A review

The photocatalytic evolution of hydrogen is a potential method for acquiring green hydrogen from nature. Unfortunately, this technique has limitations owing to a lack of knowledge of the reaction processes, despite the fact that in recent decades significant scientific adva`nces have been achieved regarding catalyst design and efficiency. Often neglected in favor of heterojunction engineering or band engineering, the chemical environment of catalysts has long been the subject of research. This article offers insight into the photocatalytic H₂ evolution from the surface reaction. It was underlined that reactant adsorption and surface charge extraction have a significant impact on the enhancement of photocatalytic H₂ evolution and anti-photocorrosion properties of the catalyst, which are also strongly connected to the catalyst's chemical environment. Specifically, this study emphasizes the significance of surface/interface condition, type and concentration of electrolytes, reaction solvents, and temperature, etc., during photocatalytic H₂ development, all of which play a crucial role in surface charge extraction of catalyst. In addition, the surface kinetics, adsorption and diffusion of reactants, the selectivity of intermediates, etc., are emphasized for designing highly efficient reaction systems in future applications of photocatalysis. It was shown that more comprehensive methodologies are urgently required for constructing efficient and stable photocatalytic reaction systems by merging catalyst design and reaction environment manipulation. This review may provide fresh ideas for the use of photocatalytic solar energy conversion.     

Charge transfer processes involved in photocatalytic hydrogen production over CuO/ZrO2–TiO2 materials

Co-catalysts are widely employed to boost the photocatalytic hydrogen production; particularly, CuO has shown a remarkable improvement in the reaction rate. However, the impact of CuO on the charge transfer process during photocatalytic water reduction has been barely investigated. In this work, ZrO₂–TiO₂ (ZT) heterojunctions (5 mol% ZrO₂) have been obtained by means of the sol–gel method. Subsequently, copper nitrate impregnations are prepared by an incipient wetness impregnation method to get 0.5, 1, 3 and 5 wt% CuO loadings. A maximum in the photocatalytic activity is observed for the material containing 1 wt% CuO, followed by a drastic drop in the hydrogen generation rate. Electrochemical characterization shows that the charge-transfer resistance controls the photocatalytic experiments together with the additional interfacial resistance. The maximum photocatalytic activity is then given by a compromise between these two parameters. A further increase of the additional resistance, directly proportional to the CuO loading, reduces drastically the photocatalytic behavior most likely due to the electron trapping at the ZT–CuO interface.     

Review on the interface engineering in the carbonaceous titania for the improved photocatalytic hydrogen production

Hydrogen is the prime source of energy with enormous attention in the current research development process as it is safe, clean, eco-friendly, and can be produced from renewable resources through simple catalytic reactions. Scalable production of hydrogen through photocatalysis has been achieved using carbon-modified semiconductors since 2009. In this direction, this review delivers comprehensive understandings into the interface and structural interactions between TiO₂ and carbonaceous materials such as carbon, carbon nanotubes, graphene, activated carbon, graphitic carbon nitride, carbon quantum dots, etc., and their influences toward improving the hydrogen generation activity of these systems. Besides, recently developed carbonaceous materials such as 3-D graphene, carbon nanohorns, and carbon nanocones have also been discussed on their character in the photocatalytic water splitting procedure. In general, the observed improvements in this carbon-modified TiO₂ attributed to the synergetic effects, which offer the active migration of charge carriers and reduced recombination rates in the photocatalyst. Finally, highlighting the future perspectives of the carbonaceous materials in photocatalytic applications are concluded.     

Analysis of multilayer convective flow of a hybrid nanofluid in porous medium sandwiched between the layers of nanofluid

AgBr acts as a good sensitizer for titanium oxide, hence TiO₂–AgBr nanoparticles exhibit high photocatalytic activity which helps decompose methyl orange under visible light irradiation. Methyl orange is a chemical compound that is hard to degrade and has high stability. It is photoreactive and can capture photons from the sun and is highly used as a light harvester in solar cells, hence, it is used in solar applications. In view of this, the present article deals with the analysis of heat transfer in a multilayer flow of two immiscible nanofluids in a vertical channel that finds application in the fields of solar reactors, electronic cooling, and so on. The mathematical model involving the effect of thermal radiation and the presence of heat source is in the form of a system of ordinary differential equations. This system of equations is simplified using the differential transform method-Padé approximant and the resulting equations are solved algebraically. It is observed that the temperature of the coolant does not reach its saturation point faster due to the presence of different base fluids that differ in their thermal conductivity. This helps in maintaining the optimum temperature of the system.     

Detailed modelling of photon recycling: application to GaAs solar cells

The re-absorption of photons emitted in a semiconductor material as a consequence of radiative recombinations, a process referred to as photon recycling (PR), has been researched into for several decades because of its primary influence in increasing the minority carrier lifetime and related parameters. Solar cells with direct bandgap materials and high-absorption coefficients are firm candidates to show PR effects, leading to an improvement in the conversion efficiency of up to 1–2% in absolute terms for cells with conventional designs. However, the formal modelling of PR effects requires the inclusion of additional terms in the standard set of semiconductor equations and researchers usually tend to neglect its influence, because of the lack of available tools for an easy evaluation of this phenomenon in their particular devices. This paper describes a detailed model of PR which allows the incorporation of specific characteristics and optics of GaAs solar cells and, at the same time, solves some of the problems found in previous developments of these numerical models. The methodology for the calculation is based on the use of commercially available programs for semiconductor device simulation that do not initially have the potential for PR modelling and, thus, it can be extended to and applied by other researchers whishing to compare its relative influence on the performance of different structures and materials.     

Factors affecting photocatalytic performance through the evolution of the properties due to the phase transition from NaBiO3·2H2O to BiO2–x

The phase transition process of a photocatalytic system from NaBiO₃·2H₂O to BiO_2–x has been investigated to understand the important factors that affect photocatalytic performance in a composite system. It is found that a proper amount of BiO_2–x on the surface of NaBiO₃·2H₂O could effectively suppress the electron/hole recombination and increase the exposed reactive sites for photocatalytic reaction. A fully covered BiO_2–x on NaBiO₃·2H₂O results in a dramatical decrease of photocatalytic degradation of dye. An over long hydrothermal process can result in BiO_2–x with reduced oxygen vacancies, which degrades the photocatalytic activity. Furthermore, the photocatalytic reduction ability of CO₂ conversion has been investigated, indicating that the surface activity to different reactants also directly affects the catalytic performance. The investigation of the gradient phase transition process presents a clear guidance to construct a desired photocatalytic system, in addition to selecting gradient materials with suitable bandgap structure and a morphology with different fraction and distribution of each component. The defect evolution of each component during construction of a composite is also an important factor that should be optimized and considered in making a composite to achieve high photocatalytic efficiency.     

Single-atom catalysts for photocatalytic hydrogen evolution: A review

The application of hydrogen energy is significant to meet the challenge of fossil energy depletion and carbon emission limitation. The photocatalytic hydrogen evolution has been considered as a green and clean strategy for obtaining hydrogen. However, due to the high cost and limited efficiency, photocatalysis is only considered as one of the candidate methods for hydrogen production. Recently, several researchers have devoted to develop the single-atom catalysts (SACs) as promising cocatalysts and found great potential applications that are distributed across the fields of energy and environmental science. SACs exhibit several advantages, including abundant active sites, efficient photo-generated carrier recombination, atom-economic reaction mechanism, etc. In this synthetic review, we have summarized the advances of SACs in photocatalytic hydrogen evolution. Firstly, the synthesis strategies and characterization methods of SACs have been introduced. Then, the approaches for immobilizing prepared SACs on various supports have been elucidated. Finally, the photocatalytic activity of representative SACs-loaded supports has been analyzed, as well as the modification routes for enhancing performance. The review aims to record the development and applications of SACs in the field of photocatalytic hydrogen evolution. More studies are still required to clarify the mechanism of SACs based photocatalytic reactions, thus guiding the design of SACs-support system.     

Radiation energy transfer and maximum conversion efficiency

Radiation energy transfer is modeled as the enthalpy flux of photons across the boundary of a thermodynamic system. It is proved that this energy transfer process can be treated as heat transfer. Compression work must be applied to the system to push the photons out. The energy transfer rate and maximum conversion efficiency computed from the model are identical to those determined from the Stefan–Boltzmann law and the Carnot efficiency for blackbody radiation.     

A critical review on core/shell-based nanostructured photocatalysts for improved hydrogen generation

Photocatalytic water splitting into gaseous hydrogen and oxygen in the presence of semiconductor photocatalysts under a visible spectrum of solar irradiation is one of the most promising processes for plummeting energy demands and environmental pollution. Among the successful photocatalytic materials, the core/shell nanostructures show promising results owing to their fascinating morphology that protects the surface features of the core besides the effective separation of photo-excitons resulting in an enhanced rate of hydrogen production up to 162 mmol h⁻¹g⁻¹_cat, which is a notable highest value reported in the literature. In this review, we have focused on the basic characteristics of the core-shell structure-based semiconductor photocatalytic systems and their efficient water-splitting reactions under light irradiation. Comprehensive detail on various synthesis methods of core-shell nanostructures, shell thickness-dependent properties, charge-transfer reaction mechanisms, and photocatalytic stability are highlighted in this review. Core-shell nanostructured materials have been extensively used as a photocatalyst, co-catalyst, and by coupling with supporting materials to improve the apparent quantum efficiency up to 45.6%. Besides, important photocatalytic properties that influence the redox reactions i.e., effective exciton separation, the effect of different light sources/wavelengths, surface charge modeling, photocatalytic active sites, and turnover frequency (TOF) have also been focused on and extensively described. Finally, the present and future prospects of the core-shell nanostructured photocatalysts for solar energy conversion into green hydrogen production have been expounded.     

Photocatalysis and radiation absorption in a solar plant

Recently, many papers have appeared in literature about photocatalytic detoxification. However, progress from laboratory data to the industrial solar reactor is not easy. Kinetic models for heterogeneous catalysis can be used to describe the photocatalytic processes, but luminic steps, related to the radiation, have to be added to the physical and chemical steps considered in heterogeneous catalysis. Thus, the evaluation of the radiation, and its distribution, inside a photocatalytic reactor is essential to extrapolate results from laboratory to outdoor experiments and to compare the efficiency of different installations. This study attempts to validate the experimental set up and theoretical data treatment for this purpose in a Solar Pilot Plant. The procedure consists of the calibration of different sunlight radiometers, the estimation of the radiation inside the reactor, and the validation of the results by actinometric experiments. Finally, a comparison between kinetic constants, for the same reaction in the laboratory (artificial light) and field conditions (sun light), is performed to demonstrate the advantages of knowing the radiation inside a large photochemical reactor.