With the rapid development of industrialization and the economy, a large amount of volatile organic compounds (VOCs) are emitted into the atmosphere. These sources of pollution not only come from outdoor factors such as fuel combustion, vehicle exhaust, and industrial emissions but also include indoor pollution from kitchen oil fumes and building decoration materials[1]. Currently, industrial methods for removing VOCs from the atmosphere commonly include absorption-adsorption[2-3], condensation[4], biodegradation[5], thermal incineration[6], catalytic oxidation[7-8], and membrane separation[9-10]. However, these technologies face challenges such as high initial costs, large energy consumption, and processing difficulties. Therefore, developing efficient and environmentally friendly new technologies for VOCs degradation is particularly necessary, which has significant value for improving air quality and protecting public health in our country.
Photocatalysis is an emerging green energy conversion technology[11] that has attracted widespread attention both domestically and internationally. It uses semiconductor photocatalysts to directly utilize solar energy to remove environmental pollutants under mild conditions, offering advantages such as low energy consumption, environmental friendliness, and convenience[12].
Photocatalytic degradation of VOCs falls under photocatalytic oxidation technology (PCO), and its reaction mechanism is shown in Figure 1. Semiconductor materials with suitable bandgap energy (such as TiO₂) are irradiated with sufficiently energetic light to excite electrons from the valence band (VB) to the conduction band (CB) and generate electron-hole pairs (e⁻ and h⁺). The photogenerated electrons and holes then react with water, surface hydroxyls, and O₂, generating active free radicals such as hydroxyl radicals (·OH) and superoxide radicals (·O₂⁻). These radicals oxidize and decompose the VOCs molecules adsorbed on the catalyst's surface into CO₂, H₂O, and other lightweight byproducts.
Figure 1. TiO₂ Photocatalytic Degradation of VOCs Reaction Mechanism[13]
The photocatalytic degradation process of VOCs is quite complex and is influenced by various factors such as light intensity, catalyst properties, VOCs concentration, and reaction humidity. Temperature is also an important factor affecting the reaction kinetics in photocatalysis[14]. Currently, research on the effect of temperature on catalysis during photocatalysis mainly focuses on the synergistic effect of photo-thermal catalysis. Li et al.[15] found solar-driven CeO₂ thermal catalysis on TiO₂/CeO₂ nanocomposites, which exhibited stronger catalytic activity for benzene oxidation under xenon lamp irradiation.
Photo-thermal catalysis utilizes solar energy to provide energy for catalytic reactions while using UV-vis to excite semiconductor catalysts and the thermal effects of infrared light. This allows for more efficient use of the solar spectrum, achieving high-efficiency degradation of pollutants while reducing energy consumption, making it a promising method for pollutant degradation.
1. Light excitation and thermal activation: Photo-thermal catalysts absorb photons under light irradiation, causing electrons to transition to higher energy levels and form electron-hole pairs. At the same time, thermal energy activates the catalyst surface, increasing the activation energy and promoting the reaction process.[16]
2. Reactant adsorption: VOCs molecules adsorb onto the photo-thermal catalyst surface. At high temperatures, adsorption efficiency increases, enhancing the contact between the reactants and the catalyst.[17]
3. Free radical generation: Excited electrons and holes migrate to the catalyst surface, reacting with adsorbed oxygen and water molecules to generate active oxygen species such as hydroxyl radicals (·OH) and superoxide anion radicals (·O₂⁻). These free radicals have strong oxidative capabilities against VOCs.[18]
4. VOCs oxidation and degradation: These active oxygen species attack VOCs molecules, breaking their chemical bonds and converting them into harmless small molecules such as CO₂ and H₂O.[19]
5. Product desorption: Finally, the products generated from the reaction desorb from the catalyst surface, releasing active sites of the catalyst and preparing for a new reaction cycle.[20]
Figure 2. Photo-thermal Catalysis Mechanism Diagram[21]
PerfectLight provides the following solutions in the field of photocatalytic (thermal) VOCs degradation:
PLR-RP/RT Series Photo-thermal/(Thermal) Catalysis Reaction Evaluation Devices are suitable for various types of gas-solid phase photo/photo-thermal/thermal catalytic reactions.
The device is equipped with a unique and innovative circumferential illumination reactor, with the catalyst loaded around the light source, effectively increasing the light-illuminated area of the catalyst from 0.3 cm² in planar illumination to approximately 20 cm², allowing the catalyst to fully contact with light. At the same time, under the premise of ensuring effective light penetration, the catalyst loading is increased from 0.9 mL to 9 mL, which improves light utilization efficiency and also enhances the substrate's adsorption and conversion rate.
The device features four major functional modules: liquid delivery - vaporization - pipeline heating - condensation separation.
Liquid delivery system ensures a constant amount of liquid enters the preheating chamber;
Preheating chamber adopts a special vaporizer structure design to effectively avoid problems such as large vaporizer volume, unstable gas output after vaporization, and inability to vaporize in real-time, ensuring a stable output of liquid vaporized mixed gas;
Pipeline heating structure effectively prevents condensation of the liquid before entering the reaction chamber;
The condensation separation system rapidly condenses unreacted liquid raw materials and reaction-generated liquid products into a separator for collection, for subsequent reaction process analysis.
For different reaction temperature and pressure conditions, the device is available in various specifications:
High-pressure version (~650℃, ~10 MPa)
Standard version (~850℃, ~6 MPa)
High-temperature version (~1050℃, ~3 MPa)
High-temperature high-pressure version (~850℃, ~10 MPa)
If the above configuration still cannot meet the reaction requirements, PerfectLight also offers customization services for the device (Consultation Phone: 400-1161-365)
PLR-PTSRⅡ Photothermal Catalysis Reactor primarily utilizes flow differential reactions while accommodating closed integral reaction needs. It features in-situ heating, dual flowmeter pressure control, dual detectors for temperature measurement, and allows water vapor to participate in the reaction, providing a photothermal cooperative reaction testing platform with controllable flow and pressure.
PLR-GPTR Series Gas-Solid Phase Photothermal Reactors are compact devices: compatible with various detection equipment; supports closed/circulation gas circuit modes; optimizes catalyst loading platform for better gas-catalyst contact; equipped with high-pressure metal quick connectors for multi-segment program automatic temperature control; customizable for different volumes and integrated water bath temperature control.
PLC-GDHC I Gas Diffusion Multiphase Continuous Catalytic Reaction Platform provides the gas-solid phase photocatalytic continuous conversion process scheme:
① Gas Diffusion Reactor: Contains a porous hydrophobic gas diffusion layer that can be loaded with photocatalysts; effectively solves the issue of liquid water shielding photocatalyst active sites and avoids hydrogen evolution.
② Gas Diffusion Circulator: Provides circulation power for the raw gas atmosphere; offers external power to promptly desorb products from the photocatalyst interface; recirculates unreacted raw gas for gas-solid heterogeneous reactions.
③ Integrated Electric Lift Light Source: Equipped with a white high-power LED light source with replaceable/adjustable/customizable wavelength bands; electric lift design allows fine adjustment of light source irradiation distance.
④ Modular Function Platform: Optional heating modules, bottom illumination photoelectric modules, and temperature control sensor modules; compatible with various gas diffusion reactors to expand different reaction types.
In scientific research, screening reaction conditions, catalyst preparation conditions, and reaction results for photochemical processes is a time-consuming and labor-intensive task. Additionally, manual operation and asynchronous experiments inevitably cause slight variations in results. Based on these application needs, MCP-WS1000 Photochemical Workstation has been developed for systematic optimization of reaction conditions and rapid catalyst screening.
MCP-WS1000 Photochemical Workstation consists of PCX-50C Discover Multichannel Photocatalytic Reaction System, PLA-MAC1005 Multi-Channel Atmosphere Controller, PLA-GPA1000 Fully Automatic Sampler, and an adaptable Characterization Testing System.
PCX-50C Discover Multichannel Photocatalytic Reaction System offers customizable and combinable light output wavelengths ranging from ultraviolet to infrared, with continuously adjustable light intensity; it can be paired with reaction vessels of different volumes to enhance light utilization and reaction rates, enabling independent control and screening of light intensity, wavelength, temperature, and other reaction condition parameters for each channel.
Combined with the PLA-MAC1005 Multi-Channel Atmosphere Controller, it can screen gas atmosphere, reaction pressure, and other conditions, perform multiple gas replacements and pressure adjustments within the vessel, and monitor gas pressure variations in different reaction channels with real-time display and recording.
PLA-GPA1000 Fully Automatic Sampler automates sampling, delivery, and injection processes, standardizing experimental procedures and improving efficiency while reducing human error. The sampling process is protected by carrier gas to effectively avoid interference from air in photocatalytic CO₂ reduction tests, and it is compatible with mainstream gas chromatographs as well as headspace samplers.
Further integration with microfluidic systems and detection chips can expand testing methods to various spectroscopy and imaging techniques, allowing for online, offline, and in-situ characterization of reaction processes.
Photocatalysis and photothermal catalysis technologies provide innovative solutions for the efficient and environmentally friendly treatment of volatile organic compounds (VOCs). PerfectLight is committed to advancing research and technological innovation to achieve long-term goals of green and sustainable development.
