Heterogeneous Ozone Catalysts: Boosters for the Strong Oxidation Engine of Water Treatment
Advanced oxidation technology, with its core weapon of strongly oxidising hydroxyl radicals (·OH), has become a key means of degrading stubborn organic pollutants in water. These radicals have a very high oxidation potential (2.80 V) and can non-selectively mineralise complex organics into harmless carbon dioxide and water. Ozone itself, however, has clear shortcomings: its direct reaction rate constant with most organics is low (typically only 0.1-10 L·mol⁻¹·s⁻¹), and its solubility and chemical stability in water are both unsatisfactory (solubility about 570 mg/L at 20°C; half-life only about 20 minutes). This limits the effectiveness of ozone used alone and has made heterogeneous ozone catalysts the key to raising the efficiency of the whole advanced oxidation process.
A heterogeneous ozone catalyst is a catalytic material that exists in the catalytic reaction system in a different physical phase from ozone (gas or liquid phase) and the water being treated (liquid phase). They are usually solids, and through multiphase interfacial contact with gaseous or dissolved ozone and with liquid-phase pollutants they markedly accelerate the chain of ozone conversion to hydroxyl radicals, amplifying the oxidation performance.
SINOKLE ozone catalyst
Researchers currently focus on heterogeneous ozone catalysts built on different supports, each with its own features and challenges:
Metal oxide catalysts (such as Al₂O₃, TiO₂, MnO₂, Fe₂O₃ and their composites): These catalysts generally show high intrinsic catalytic activity and satisfactory structural stability. However, their large-scale use is often constrained by the cost of precious-metal components such as Pt and Ru. In addition, some metal oxides such as iron oxides are easily inhibited by coexisting anions (phosphate, carbonate) in complex water matrices or suffer metal ion leaching, which not only lowers efficiency but may cause secondary pollution.
Zeolite-based catalysts (such as ZSM-5 and metal-loaded Y zeolite): Zeolites offer excellent thermal stability and unique selective catalysis thanks to their regular crystal structure and tunable pore system. But their synthesis is complex and energy-intensive, keeping overall costs high. More importantly, during prolonged operation or under extreme conditions the active sites are easily covered by impurities in the water or lost with framework aluminium, causing irreversible deactivation.
Carbon-based catalysts (activated carbon AC, carbon nanotubes CNTs, graphene and their derivatives): Catalysts built on carbon materials are showing remarkable combined advantages:
Huge specific surface area: carbon materials (activated carbon reaches 1000-3000 m²/g, graphene a theoretical value of about 2630 m²/g) act like a vast battlefield, providing enormous numbers of active sites for the enrichment of ozone molecules and pollutants and for catalytic reaction, greatly improving interfacial reaction efficiency.
Excellent chemical inertness: across a wide pH range and in oxidising environments the carbon framework is highly tolerant, resisting corrosion or destruction by the reaction medium and ensuring long-term operational reliability.
Designable pore structure: fine control of synthesis and activation (for example tuning the micro/mesopore ratio of activated carbon or designing carbon nanotube arrays) optimises the mass transfer path of reactants and the distribution of active sites, thereby improving catalytic performance in a targeted way.
Environmentally friendly: carbon sources are abundant (biomass, minerals), preparation is relatively green, and spent carbon materials carry low environmental risk, in line with sustainable development.
Outstanding recyclability: most carbon-based catalysts can be regenerated effectively by simple heat treatment or washing, markedly reducing operating costs and resource consumption.
Overall comparison shows that: heterogeneous ozone catalysts supported on carbon materials achieve a better balance among effectiveness, stability, economy and environmental friendliness thanks to their unique physicochemical properties, and represent an important development direction.
The core advantages of carbon catalysts stem from their intrinsic properties. A high specific surface area builds an efficient 'reaction platform'; excellent conductivity (graphene carrier mobility can reach 200,000 cm²·V⁻¹·s⁻¹) promotes electron transfer and accelerates ozone activation; and strong chemical stability is the cornerstone of durability. Whether used as a support (for example carrying metal nanoparticles) or as the active catalyst itself (oxygen-containing functional groups and structural defects can also catalyse), carbon materials strongly adsorb and enrich trace organic pollutants in water, shortening the 'distance' to the reactive species. More importantly, they efficiently promote chain decomposition of ozone on their surface (O₃ → O₂ + O; O+ H₂O → 2·OH), continuously generating a high concentration of hydroxyl radicals and achieving deep mineralisation of pollutants.
SINOKLE carbon-based ozone catalyst
Heterogeneous ozone catalysts, and especially the ever-improving carbon-based catalysts, have therefore become the key to unlocking the full potential of advanced ozone oxidation. Through precise catalytic engineering at multiphase interfaces they markedly overcome the limitations of ozone itself, providing strong technical support for more efficient, more economical and greener deep purification of water and continuously driving innovation in water treatment.
