The use of fossil fuels, industrialisation, and human civilisation have all made the air, water, and land very dirty. Pesticides, industrial chemicals, medicinal and personal care products, organic dyes, and burning leftovers have been used in harmful ways over the past few decades, causing them to build up in the environment. Many businesses, like cloth, furniture, food, and paint, use organic dyes. About 30 to 40 percent of these colouring agents end up in waterways, which is bad for the environment and people’s health. Some water-soluble dyes keep marine life from getting hurt by the sun, while others break down and release chemicals that are cancer-causing.
Scientists are looking for new energy sources and better ways to stop pollution because fossil fuels are running out and pollution is getting worse. As a long-term and inexpensive way to clean up the environment and meet the demand for green energy, solar energy can be used. Some of the old ways of treating wastewater, like coagulation, microbial decay, absorption of activated carbon, burning, filtration, and sedimentation, are no longer cost-effective or leave behind secondary pollution. Photocatalytic oxidation with a semiconducting material as a catalyst, ultrasonic cavitation, electron beam irradiation, Fenton’s reaction, and reactions with O3/H2O2, UV/O3, and UV/H2O2 have all been shown to quickly and effectively remove organic pollution.
Heterogeneous Photocatalysis—Semiconductor Oxides
as Photocatalysts
A chemical or biological process can happen on the surface of an artificial semiconductor. This is called heterogeneous photocatalysis. It works by shining light on the catalyst and the reactants or pollutants to make electrons and holes. This starts reactions that make useful products or break down pollutants into less dangerous results. A phase-pure, well-crystallized, monodisperse, nano-sized semiconductor oxide with a uniform shape is perfect for photocatalysts that work well and are stable chemically. A photocatalytic reaction’s effectiveness relies on things like the crystallite size, surface area, band gap energy, recombination rate of the photogenerated electron-hole pair, the type of reactant or pollution, and the type of active sites on the catalyst. The photocatalyst needs to have certain semiconducting properties, like being able to absorb visible light from the sun, separate photoexcited electrons from reactive holes, keep energy losses from charge transport and recombination to a minimum, be chemically stable against corrosion and photo-corrosion in water, have good electron transfer properties from the photocatalytic surface of water, and be easy and cheap to make.
Mechanism of Semiconductor Photocatalysis
When a semiconductor receives more light energy than its band gap energy, an electron moves from the valence band to the conduction band. This is called semiconductor photocatalysis. Excitons, which are made up of electrons and holes, either join together again or move to the top of the semiconductor during this process. With bound species like H2O and O2, these electrons and holes take part in different oxidation and reduction processes. The main processes that happen during photocatalytic hydrogen production and the breakdown of pollution are oxidation and reduction. Photocatalytic water splitting processes use photoexcited electrons in the conduction band to react with water and make H2 and OH-. The semiconductor’s conduction band level needs to be lower than the reduction potential of H2 (H+/H2) and its valence band level needs to be higher than the oxygenation potential of O2 in order to start making hydrogen and oxygen. But, different model polluters and photocatalysts have a big effect on the photocatalytic breakdown process. The photoactivity and decay path are determined by the main radical species.
Methods to Tailor the Photocatalytic Properties
of Semiconductor Photocatalysts
Since it was found that water can be split into hydrogen and oxygen using a semiconductor (TiO2) electrode and UV light, a lot of work has been done to make hydrogen from water splitting using different semiconductor photocatalysts. Because about 45% of sunlight is visible, it is important to create semiconducting photocatalysts that use this part of sunlight to start photocatalytic processes. One good way to increase the light reaction range of a material is to change its chemical makeup and control its electronic band structure.
To change a semiconductor material from having a wide band gap to a narrow band gap, metal and nonmetal substitutions are being thought about. By replacing metal ions, impurities are created in the banned band. These impurities lower the photocatalyst’s band gap energy, which moves the catalyst’s photo-response towards the visible region. Many papers have talked about how metal ion doping can be used to change wide band gap photocatalysts so that they can react with visible light.
Adding nonmetal ions like N3−, S2−, and F− is another way to close the band gap and make photocatalysis work better. Nonmetal ion dopants are less likely to form donor levels in the forbidden band and recombination centres than metal ion dopants. This makes anion doping a better way to boost photocatalytic activity.
However, visible light-triggered photocatalytic processes have two big problems: electron/hole pairs recombine quickly, and high-level energy electrons (HLEEs) driven by visible light are not used very much. These problems can be fixed by making new photocatalysts, like a metal/nonmetal doped photocatalyst, a noble metal surface-modified photocatalyst, a dye/semiconductor-sensitized photocatalyst, and a p–n heterojunction structure composite photocatalyst.
Photocatalysts that are filled with metals and nonmetals, like Pt-loaded photocatalysts, have good photocatalytic qualities because they narrow the band gap and slow down the rate at which photogenerated electron-hole pairs combine back together. However, p–n heterojunction photocatalysis can start the reduction and oxidation processes by moving photoinduced electrons to the conduction band (CB) of the n-type semiconductor and holes to the valence band (VB) of the p-type semiconductor.
High-level energy electrons (HLEEs) of narrow band gap semiconductors like Fe2O3, BiVO4, and BiFeO3 can move thermodynamically to the conduction band of TiO2. This makes photogenerated charge carriers last longer and improves the uses of visible light. Graphitic carbon nitride (g–C3N4) has recently been used as an n-type semiconductor that doesn’t contain any metals to improve the photocatalytic performance of materials that aren’t very good at it. This is because it has the unique properties of being water-friendly and having a large specific surface area.
A Short Overview of Perovskite Oxides
as Photocatalysts
Oxide semiconductors have been studied a lot as photocatalysts because they are cheap, easy to make, poisonous, and have qualities that can be changed. A lot of research has been done on oxides such as TiO2, ZnO, WO3, vanadates (VO4), and molybdates. Scientists are interested in the perovskite family with the general formula ABO3 because they have interesting structures, unique qualities, and can be put together in a variety of ways. These oxides are very stable chemically and have a wide range of electrical and ionic conductivities. They also have multiferroicity behaviour, the ability to change from order to disorder, and a high level of chemical stability.
The structure of perovskite oxides (ABO3) is unique, which helps their photocatalytic activity. The B–O–B bond angle is related to energy delocalisation. The closer it is to 180°, the easier it is for the excited energy to move around, which results in more photoactivity. Photoactivity should be higher in materials from the ABO3 family that have an ideal perovskite structure.
New studies on the photocatalytic activity of ABO3-based perovskite-type materials have led to the creation of a wide range of new compounds. Review papers have been written about perovskite materials, including their structure, how they are made, and how they can be used in different areas. Ewelina Grabowska talked about how to make perovskite oxides, how to characterise them, and how to improve their photocatalytic activity. Guan et al. talked about the latest progress in perovskite materials and how they can be used in photocatalytic processes to split water and clean up the environment.
Scientists have also looked into how to use changed ABO3 photocatalysts to make AxByOz photocatalysts. Wei et al. talked about the basic ideas behind the water splitting process, how organic dyes break down in sunlight, and solar cells. They also talked about what photocatalysts need to do their job well. Zhu et al. looked at how well different types of perovskite oxides work as catalysts for processes in gas, solid, and liquid phases.
Recent Developments in Enhancing the Photocatalytic
Activity of Perovskite Materials
The review talks about the photocatalytic activity of lanthanum-based perovskites LaMO3 (M = Fe, Co, and Mn) and BaMO3 (M = Zr and Sn). It also talks about new ways to improve the photocatalytic behaviour of perovskites based on alkali and alkaline earth metals (ATiO3, ATaO3, and ANbO3). It has been shown in both experiments and theory that LaMO3 is a good photocatalyst because of its unique crystal structure, ability to carry electricity, and great optical qualities. LaFeO3 doesn’t work very well as a photocatalyst, though, because it doesn’t absorb visible light very well and doesn’t use high-level electrons excited by visible light very well.
To make the photocatalytic features of LaFeO3 nanoparticles better, different techniques have been used, such as sol–gel, sonochemical, electrospinning, the polymeric precursor route, and hydrothermal methods. Shudan Li and Xianlei Wang used electrospinning to make one-dimensional LaFeO3 fibres with different shapes. They then studied how the shape affected the photocatalytic activity. Putting metal ions in place of La/Fe in LaFeO3 also made it more photocatalytic.
The researchers by Parrino and others made Cu-substituted LaFeO3 perovskites (LaFe1xCuxO3d) using the citrate auto-combustion method and talked about how they could be used as photocatalysts by using 2-propanol oxidation as a probe reaction in the gas–solid regime. They came to the conclusion that adding more copper to Cu(II)-substituted LaFeO3 made it more photocatalytic, but adding more copper than 10 mol% made it less effective. Higher copper contents made it less effective overall.
We found that Cu(II)-substituted LaFeO3 was more active than pure LaFeO3 because it had oxygen holes and less electron–hole exchange. The manganese-substituted LaFeO3 was a much better catalyst than pure LaFeO3 because it had more oxygen holes, Mn ions with changeable valency, and a strong ability to absorb visible light. It was reported by Jauher et al. that they made LaMnxFe1−xO3 and tested how well it broke down cationic and anionic dyes with and without visible light.
Xicai Hao and Yongcai Zhang used a gel combustion method to make porous nano-LaFeO3 and then looked into how visible light can help reduce Cr(VI) in water. Giuseppina et al. made LaFeO3 nanoparticles using a solution burning method and studied how well they could produce hydrogen from a glucose solution in water under UV and visible light from light-emitting diodes.
The study looks into how 15-nm-wide LaFeO3 nanoparticles with a band gap of 1.86 eV can be used as catalysts to break down methylene blue (MB) or rhodamine B when exposed to visible light. The researchers found that the oxidation process was mostly controlled by the transfer of electrons from the dye molecule to the hole.
Muhammad et al. made ZnO-coupled Bi-doped porous LaFeO3 and tested how well it could break down 2,4-dichlorophenol (2,4-DCP) and change CO2 using visible light. The better activity in visible light is due to better use of high-level electrons excited by visible light. This is done by slowing down the absorption of visible light through the Bi-introduced surface states and connecting ZnO to create a good high-level energy base for taking electrons.
Yan et al. made a p–n heterojunction out of p-type LaFeO3 and n-type g–C3N4, and they tested how well it could break down Brilliant Blue (BB) when exposed to visible light. The better photoactivity of g–C3N4 and LaFeO3 is due to better separation of electron–hole pairs, more superoxide and hydroxyl radicals, and a Z-scheme photogenerated electron transfer mechanism that works with the dye-sensitization effect of the photocatalytic reaction process.
LaCoO3, a perovskite with interesting physical and chemical qualities, was used to improve the production of hydrogen from a formaldehyde solution in water at low temperatures and without adding any other chemicals. The heterojunction structure greatly improved the formation of charges, the absorption of visible light, and the effective confinement of the exchange of photogenerated electron–hole pairs, resulting in higher photocatalytic activity.
Minghui Wu et al. made LaCoO3 that worked well by adding oxygen vacancies to it using natural sugarcane bagasse that had oxygen vacancies that could be changed. This method not only replaces standard chemical reactions, but it also gives a lot of functional groups that can interact with metal ions. This creates photocatalysts with different surface qualities and unique structures.
Researchers have looked into the link between biomass-induced oxygen vacancies on perovskite and how well it produces hydrogen through photocatalysis. As-synthesized sugarcane bagasse-mediated LaCoO3 perovskite worked better than that made using the traditional citric acid method to make hydrogen from formaldehyde solution when exposed to visible light. Liqing et al. reported a new way for microbes to make a highly effective Cu-doped LaCoO3 photocatalyst from Pichia pastoris GS115 for making hydrogen from a formaldehyde solution when exposed to visible light. Copper doping helps make the right amount of impurities and oxygen vacancies, and adding biomass during the synthesis process changes the crystal structure and surface structure of the catalyst, affecting the diffraction angle and unit cell while also controlling oxygen defects on the surface.
Jayapandi et al. made pure LaCoO3 and silver (Ag)-modified LaCoO3 using a chemical process. Ag is thought to be a better metal dopant because it can help charge carriers move, remove carbon effectively, absorb light better, and provide active species for oxygen activation. Ag-modified LaCoO3 broke down methylene blue (MB) faster than pure LaCoO3 (99% in 10 minutes).
To boost photocatalytic activity, porous perovskite oxides with more specific surface area are very important. Rajesh Kumar et al. studied how different shapes of LaMnO3 particles affect the breakdown of RB dye when exposed to visible light. They discovered that the porous shape and specific surface area are very important for the photocatalytic performance. Peisong et al. looked into how YbFeO3 and EuFeO3 could be used to break down methyl orange dye when exposed to visible light.
For a long time, titanium-based perovskite materials made up of ATiO3 (A = Sr, Ca, and Ba) have been researched for use in photocatalytic processes because they are very stable at high temperatures and don’t corrode easily when exposed to light. SrTiO3 is one of the photocatalysts that has been studied the most because it has unusual photocatalytic activity in a number of different photocatalytic uses. New discoveries that make the photocatalytic uses of ATiO3 better have been shown.
Xian et al. made a group of Au/SrTiO3 nanocomposites using a photocatalytic reduction method. They then tested these nanocomposites on the photocatalytic breakdown of acid orange 7 and methyl orange dyes in the presence of real sunlight and visible light. The mixed materials were more photoactive than SrTiO3 alone. Liu et al. were able to make WO3 nanosheets with different amounts of SrTiO3 (La, Cr) and studied how methylene blue breaks down when exposed to visible light. Kissa et al. made a SrTi1-−xRhxO3 photocatalyst with different Ti/Rh ratios using a one-step chemical method and looked at how it broke down methyl orange when it was exposed to visible light. Devi et al. used a sol–gel method to make pure TiO2, SrTiO3, and SrTiO3/TiO2 hybrid. They tested the photoactivity of the samples by shining UV light on them and seeing how quickly 4-Nitrophenol (4-NP) broke down.
In their study, Swapna et al. looked at how SrTiO3 catalysts can break down methylene blue under UV light. Silva et al. used a polymeric precursor method to make SrTiOx photocatalysts that were changed with Mg. Pure SrTiO3 isn’t a good photocatalyst because it’s only active when exposed to UV light. To make SrTiO3 work with visible light, cationic and anionic dopants are often added. Co, Fe, and Ni were used as dopants by Kou et al. to improve the photocatalytic reduction of CO2 to CH4. Luo and his colleagues described three types of photocatalysts that contain SrTiO3 and can reduce CO2 with H2O vapour when exposed to visible light.
Researchers led by Shoji made strontium titanate (SrTiO3: STO) nanorod thin films that were filled with amorphous copper oxide (CuOx) nanoclusters. They discovered that adding CuOx-cocatalysts to STO nanorods improved the process of turning carbon dioxide (CO2) into carbon monoxide (CO) using water as an electron source. It was found that photocatalysts with a three-dimensional (3D) porous microsphere structure worked very well as photocatalysts because they have a large specific surface area, many active sites for the reaction of interest, absorb more light through the reflection of pore walls, and are simple to recycle by mechanical filtration. Using a sol–gel method, Yang et al. made porous SrTiO3 microspheres and saw how well they worked as photocatalysts to reduce Cr(VI) when exposed to UV light.
We made LST-0.5 microspheres out of agarose gel, SrCO3 microspheres, and La2O3 microspheres using a modified sol–gel method. The shape of the LST-0.5 sample showed higher photocatalytic activity than the undoped SrTiO3 sample for reducing Cr(VI) when exposed to visible light. The LST-0.5 sample can be used again and again, which could be a good start for their actual use.
Calcium titanate (CaTiO3) was first found in the Ural Mountains in 1839. It has since become very popular in oxide electronics as a useful material for electronics and electrical devices and as a semiconducting material with a band gap of 3.5 eV. However, CaTiO3 isn’t often used for photocatalytic tasks because it has a wide band gap, and it can only react with UV light.
Yan et al. used surface disorder-engineered CaTiO3 as a semiconducting material for breaking down rhodamine B (RhB) photocatalytically under artificial sunlight. Irradiation of graphitic carbon nitride (g–C3N4) and CaTiO3 heterojunction photocatalysts was used to break down rhB using UV, visible, and natural sunlight. Yan et al. reported an easy chemical method for making CaTiO3 nanocuboids of fixed sizes. These were then used to break down rhodamine B under a simulation of sunlight.
Han and others made an orthorhombic CaTiO3 using solid-state, sol–gel, and chemical methods. They then tested how well it could break down methylene blue (MB) in water when visible light was shining on it. Zhang et al. looked into how well Ag–La co-doped CaTiO3 powder can release hydrogen when exposed to UV and visible light. By using an easy dipping method, Im et al. made CaTiO3@basalt fibre (BF) materials that were very good at reducing CO2 through photocatalysis. Yoshida et al. looked into the CO2 photochemical reduction properties of hybrid catalysts made of CaTiO3@basalt fibre (BF) materials. These materials contain CaTiO3 with different Ca/Ti ratios.
Barium titanate (BaTiO3) can’t be used for many photocatalytic tasks because it has a wide band gap energy that ranges from 3.7 to 3.8 eV. Selvarajan et al. made new BaTiO3–SnO2 nanocomposites using both hydrothermal and precipitation formation methods. Nageri et al. said they were able to make Mn-doped barium titanate nanotube stacks using the hydrothermal method. By shining visible light on porous LST microspheres, Thamima et al. were able to see how they reduced Cr(VI).
Because of the way their crystal and energy band structures are set up, tantalate-based semiconductor materials like alkali tantalates are used a lot in photocatalysis. For photocatalytic uses, these materials have both valence band and conduction band potentials that are good. These catalysts are the best large band gap semiconductors for use as photocatalysts because they are highly sensitive to light, safe, stable, and easy to get.
NaTaO3 (band gap energy = 4.07 eV) has gotten a lot of attention in photocatalytic uses because it is stable and has a high photocatalytic activity. Some people think it’s a good base for making visible light photocatalysts, especially when rare earth elements like La. Wang et al. found that W and N co-doped NaTaO3 was more effective at breaking down rhodamine B (RhB) when exposed to visible light than NaTaO3 that was only doped with one element. In their study, Lan et al. looked at how the La/Bi co-doped NaTaO3 and pure NaTaO3 materials broke down methylene blue when exposed to visible light.
A new NaTaO3 photocatalyst with sulphur was made by Li et al. using a simple chemical method. The photocatalytic activity of this material was tested by breaking down methyl orange (MO) and phenol. Recently, there has been more interest in NaTaO3 in water splitting reactions since it was found to have photocatalytic qualities that can split water.
We made NaTaO3-based photocatalysts that were doped with different rare earth metal ions, like Y, La, Ce, and Yb, and made sure that the ratio of rare earth metal ions stayed the same. We then tested their photoactivity by making hydrogen gas from a mixture of water and methanol (methanol was used as an electron donor) in the sun. The Y-doped NaTaO3 catalyst has been found to produce more hydrogen gas. Lopez-Juarez et al. looked into the photocatalytic activity of pure NaTaO3 and NaTaO3 doped with La in the generation of H2 under UV light. We think that the better photocatalytic activity is because graphene acts as a photosensitiser in the rGO–KTaO3 composites and p–n heterojunctions form between p-type rGO and n-type KTaO3.
The research looks into the photoactivity of different doped NaTaO3 powders, such as doped-NaTaO3 photocatalysts that are loaded with Ag. Researchers made very useful potassium tantalate (KTaO3) materials using a one-step chemical method and studied how well they worked to turn carbon dioxide into methanol when exposed to UV light. The photoactivity of KTaO3 went up as different amounts of NiOx were added, and the sample with 2 weight percent of NiO/KTaO3 showed the most methanol formation.
People have thought that niobium-based perovskite materials might be good for a number of photocatalytic uses because they have a negative potential that makes it easy for photoinduced charge carriers to move between materials. It is a well-known fact that NaNbO3 has a band gap of 2.7 eV and is a clear semiconductor. How well alkali niobates work as photocatalysts when exposed to UV light varies on the type of “A” cation. If you change the A-site in alkali niobates to an Ag ion, it lets more light through to the visible range and makes the photocatalytic activity of alkali niobates better.
Sun et al. used an easy chemical bath method to make BiOI/NaNbO3 p–n junction photocatalyst at low temperature. Researchers looked into how well the BiOI/NaNbO3 mixtures could break down MB when exposed to visible light. Chen et al. made NaNbO3 with a cubic crystal structure as a photocatalyst using an easy solvothermal method. They then used a photo-deposition process to add Ru nanoparticles to it. The photocatalytic activity of the Ru/NaNbO3 combination was much better at breaking down RhB when exposed to visible light than that of NaNbO3 that was not doped with Ru.
Liu et al. studied and compared wire- and cube-shaped NaNbO3 perovskite catalysts that had Pt added to them for making hydrogen gas and breaking down organic pollutants. They discovered that the Pt/NaNbO3 systems worked much better because they could absorb light better and separate photogenerated electron-hole pairs better. Liu et al. made single-crystalline NaNbO3 with wire- and cube-like shapes using an easy and environmentally friendly method that included both a hydrothermal and an in-site self-assembly process by finding the best temperature for hot treatment.
The study team led by Li et al. used a polymerised complex method to make three different types of NaNbO3 samples. These samples had different shapes, including cubic, orthorhombic, and mixed cubic–orthorhombic. The sample made of mixed-phase NaNbO3 was the most effective at turning CO2 into CH4.
The creation of hybrid photocatalysts, especially those containing graphitic carbon (g–C3N4), has had a big impact on study into the photocatalytic qualities of semiconductors based on niobate. Shi et al. changed the photocatalytic properties of NaNbO3/KNbO3 semiconductors in this way: they made g–C3N4/NaNbO3 nanowire heterojunction photocatalysts by adding polymeric g–C3N4 to NaNbO3 nanowires and then tested their photoactivity in reducing CO2 to CH4 under visible light. They discovered that the g–C3N4/NaNbO3 heterojunction worked better as a photocatalyst than either g–C3N4 or NaNbO3 alone.
Because it has a wide band gap energy of 3.14 eV, potassium niobate (KNbO3) has also been described as a photocatalyst that is sensitive to UV light. Raja et al. made bi-doped KNbO3 powders through a solid-state process and then used UV light to test their photocatalytic activity in breaking down methyl orange (MO) in water. The researchers discovered that Bi-doped KNbO3 broke down 2.25 times faster than pure KNbO3. This is because the Bi-doped KNbO3 had a larger BET surface area, bigger crystallites, and a different band gap.
Zhang et al. wrote about how photocatalytic H2 could be made from water-based methanol using a micro-cubic-shaped potassium niobate (KNbO3) semiconductor device and visible light. Doping wide band gap semiconductors with nitrogen is a good way to change how they absorb light. Wang et al. used a simple chemical method to get N-doped NaNbO3 nanocube-shaped powders. To test the photocatalytic activity of pure KNbO3 and KNbO3 treated with N-dopamine, they were used to split water and break down four organic pollutants when exposed to visible light.
To make hydrogen, Hong et al. created a visible-light-driven photocatalytic system with potassium niobate nanoparticles and reduced graphene oxide (KNbO3/RGO). The hybrid nanocomposite (KNbO3/RGO) had the highest H2 generation rate compared to pure potassium niobate microspheres. This was mainly because photogenerated carriers were easily separated at the heterojunction of two different semiconductors.
The study talks about different photocatalytic reactions and light source preparation conditions for different materials, such as ag-modified LaCoO3, Cu-doped LaCoO3, microbial synthesis using Pichiapastoris extract, hydrogen production from formaldehyde solution, and different sol-gel processes. A variety of tools were used, such as 125 W Xe lamps, 150 W mercury lamps, the YbFeO3 sol-gel process, the one-step microwave route, a metal halogen lamp, BaZrO3 modified with Cu2O/Bi2O3 quantum dots, high-pressure mercury lamps, SrZrO3 modified with Cu2O/Bi2O3 quantum dots, phenol photodegradation under UV–Vis and toluene, high-pressure mercury lamps, and a set of 5 Vis LEDs for gas-phase reactions.
Acid orange and methyl orange (MO) break down in sunlight and visible light as part of the photocatalytic reduction method. Nanosheets of WO3 decorated with SrTiO3 (La,Cr) are also used in this process. The sol-gel steam method is used to break down methylene blue (MB) and other things. Under UV light, the SrTiO3 polymeric precursor method is used to break down methylene blue (MB), rhodamine B (RhB), and methyl orange (MO).
There are many ways to make hydrogen, such as using sacrificial agents, sun light, co-modified SrTiO3, mixed solid-state and hydrothermal processes, and different SrTiO3 hydrothermal methods. In the photo-deposition process, CO2 is broken down with water vapour to make syngas and visible light. Using H2O to CO UV light to lower CO2 is part of the geothermal path. The g–C3N4–CaTiO3 easy mixing method is used to break down rhodamine B (RhB) when exposed to UV light.
The study looks into how different photocatalytic methods can be used to break down rhodamine B (RhB) in visible light from different light sources. The researchers used a number of different techniques, such as hydrothermal, sol-gel, and hydrothermal methods. They also used methylene blue (MB) dye in UV light.
Several types of light were used for the photocatalytic process, including visible light, Mn-doped BaTiO3 nanotube arrays, O-Chloroaniline, and the microwave-assisted peroxo method. The process involved breaking down a phenol solution, getting rid of the gaseous toluene, and making hydrogen gas in the presence of a formic acid solution.
The researchers also looked into how geothermal and calcination processes can work together. They looked at CO2 production, artificial sunshine, CuO-patched cubic NaTaO3, and carbon-doped KTaO3. They also used the solid-state method and the photo-deposition technique. The solid-state method used water as an electron source to turn CO2 into CO, and the photo-deposition technique turned CO2 into CO/H2/CH3OH/CH4.
The researchers also used the photo-deposition process along with the single-crystalline NaNbO3 hydrothermal method. This made H2 from a mixture of water and methanol and broke down rhodamine B and 4-chlorophenol. They also used the water splitting of H2 method, the g–C3N4/NaNbO3 ultrasonic dispersion method followed by heat treatment method, and the bi-doped KNbO3 solid-state reaction to change CO2 into CH4.
In conclusion, the work gives us useful information about how to use different photocatalytic ways to break down rhodamine B in visible light from different light sources.
Conclusions and Insights
Perovskite oxides with the formula ABO3 can be used to make new compounds by partially replacing metal cations in the A- and B-sites. This makes it possible to make isostructural series with different chemical and physical features. To understand the physical features of perovskites, you need to look at how the metal ions are arranged and where they are located. From the point of view of photocatalysis, these materials have a special structure that helps photocatalytic activity. The bond angle between metal, oxygen, and metal (B-O-B) in perovskite oxide is an important structure factor that needs to be thought about. It is possible to change a perovskite’s photocatalytic qualities by adding dopants to its grid and changing its electronic structure. To make new perovskites that work well, though, more work needs to be done to figure out how the electronic structure affects the photocatalytic activity. Other things, like band gap energy, crystallite size, surface area, the lack of a metal cation, and O2− anions, also have a big impact on how well perovskites oxides work as photocatalysts. The photocatalytic performance depends on the choice of preparation methods, since standard methods can damage pore structures and make the surface area small.
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