Introduction: The Growing Challenge of Water Contamination

Water contamination remains one of the most pressing environmental and public health challenges of our time. According to the World Health Organization, an estimated 2.2 billion people lack access to safely managed drinking water services, and hundreds of millions of cases of waterborne diseases are reported annually. Beyond microbial pathogens, the modern chemical landscape has introduced an array of persistent and emerging contaminants that conventional treatment plants were never designed to handle. These include pharmaceuticals, endocrine-disrupting compounds, personal care products, per- and polyfluoroalkyl substances (PFAS), pesticides, and industrial dyes. Many of these substances resist biodegradation, pass through standard filtration and chlorination processes, and accumulate in aquatic ecosystems and food chains.

Traditional water treatment methods, such as coagulation, flocculation, sedimentation, sand filtration, and chlorination, were developed more than a century ago. While they remain effective for removing suspended solids and inactivating many pathogens, they are increasingly inadequate for the complex chemical pollutants that characterize 21st-century wastewater. Activated carbon adsorption can remove some organic compounds but requires frequent regeneration and does not destroy contaminants; it merely transfers them to another phase. Advanced oxidation processes like ozonation and UV/hydrogen peroxide treatment can mineralize pollutants but often demand high energy inputs and produce undesirable byproducts. Membrane technologies such as reverse osmosis are effective but are energy-intensive and generate concentrated brine streams that are difficult to dispose of responsibly.

These limitations have spurred intense research into next-generation catalytic processes that can achieve complete mineralization of contaminants under mild conditions, using renewable energy sources and abundant, non-toxic materials. Catalysis offers a fundamentally different approach: rather than physically separating or transferring pollutants, catalytic reactions transform them into harmless end products such as carbon dioxide, water, and inorganic salts. The goal is to develop systems that are efficient, scalable, sustainable, and economically viable for both centralized and decentralized water treatment applications. This article provides a comprehensive overview of the most promising catalytic technologies under development, including photocatalytic, electrocatalytic, and advanced oxidation processes, with a focus on the role of nanomaterials and catalyst design, sustainability considerations, and the road ahead for real-world implementation.

Advances in Catalytic Technologies

The search for more effective water treatment catalysts has led to breakthroughs across multiple domains of materials science and chemical engineering. Researchers are moving beyond simple, single-component catalysts to design complex architectures that integrate multiple functionalities: light absorption, charge separation, reactive species generation, selective adsorption, and mechanical durability. The emphasis is on catalysts that can operate under ambient temperature and pressure, use solar energy or low-voltage electricity, and target a broad spectrum of pollutants simultaneously. These efforts are supported by advances in computational modeling, which allow scientists to predict catalytic activity and optimize material properties at the atomic scale before synthesis. The following subsections detail the two most active areas of catalytic water treatment research: photocatalytic processes and electrocatalytic/advanced oxidation processes.

Photocatalytic Processes

Photocatalysis relies on the ability of certain semiconductor materials to absorb light energy and generate electron-hole pairs. These photoexcited charge carriers migrate to the catalyst surface, where they participate in redox reactions with water molecules, dissolved oxygen, and adsorbed pollutants. The most intensively studied photocatalyst is titanium dioxide (TiO2), primarily in its anatase crystalline form. When illuminated with ultraviolet (UV) light (λ < 387 nm), TiO2 produces highly reactive oxygen species such as hydroxyl radicals (•OH), superoxide anions (O2•−), and hydrogen peroxide (H2O2). These species are powerful, non-selective oxidants that can attack organic molecules, ultimately breaking them down into CO2 and H2O. The underlying mechanism has been studied extensively: upon photon absorption, an electron is promoted from the valence band to the conduction band, leaving a positively charged hole in the valence band. The hole can directly oxidize pollutants or react with water to form hydroxyl radicals, while the electron reduces oxygen to superoxide. Both pathways contribute to contaminant degradation.

A major limitation of TiO2 is its wide bandgap (3.2 eV for anatase), which restricts photoactivation to the UV region, which constitutes only about 4-5% of solar irradiance at the Earth's surface. To overcome this, researchers have developed doping strategies that introduce impurity energy levels within the bandgap, allowing absorption of visible light (which makes up about 45% of the solar spectrum). Nitrogen doping has been particularly effective, as nitrogen 2p states hybridize with oxygen 2p states at the top of the valence band, narrowing the effective bandgap. Other dopants include sulfur, carbon, and transition metals such as iron, copper, and vanadium. Codoping with two or more elements can synergistically enhance visible-light activity and charge separation efficiency. For example, N-Fe codoped TiO2 has shown superior photocatalytic degradation of methylene blue and phenol under simulated sunlight compared to undoped or singly doped materials.

Beyond TiO2, a wide array of alternative photocatalysts has been investigated. Zinc oxide (ZnO) has a similar bandgap to TiO2 but offers higher electron mobility and can be synthesized in diverse morphologies including nanowires, nanorods, and nanoflowers. Bismuth-based compounds such as BiVO4, Bi2WO6, and BiOX (X = Cl, Br, I) have attracted attention due to their narrow bandgaps and excellent visible-light absorption. BiVO4 has a bandgap of about 2.4 eV and is especially promising for water oxidation and pollutant degradation under solar illumination. Graphitic carbon nitride (g-C3N4) is a metal-free polymer semiconductor with a bandgap of 2.7 eV, good thermal and chemical stability, and a layered structure that can be exfoliated into nanosheets. Its electronic properties can be tuned by controlling the degree of polymerization, introducing heteroatoms (e.g., oxygen, sulfur, phosphorus), or forming heterojunctions with other materials. Perovskite oxides, such as SrTiO3 and LaFeO3, and metal-organic frameworks (MOFs) are also being explored for photocatalytic water treatment, though many are still at an early stage of development.

The practical application of photocatalysis for water treatment requires immobilizing the catalyst on a solid support to avoid the need for post-treatment separation. Common support materials include glass plates, stainless steel meshes, ceramic membranes, activated carbon, and polymers. The catalyst can be deposited by methods such as dip-coating, spin-coating, chemical vapor deposition, electrophoretic deposition, or in-situ growth. The reactor design is also critical: slurry reactors, where the catalyst is suspended in the water, offer high surface area but require an additional filtration step; fixed-bed reactors with immobilized catalyst layers eliminate this step but may suffer from mass transfer limitations. Compound parabolic collectors (CPCs) and other non-concentrating solar reactors have been successfully demonstrated for treating real industrial and municipal wastewater at pilot scale.

Recent research horizons include Z-scheme heterojunctions, which mimic natural photosynthesis by using two semiconductors with staggered band positions to achieve efficient charge separation while maintaining strong redox potential. For example, combining TiO2 with Cu2O or BiVO4 with WO3 creates a Z-scheme configuration where electrons from the low-potential semiconductor recombine with holes from the high-potential semiconductor, leaving electrons and holes in the favorable positions for reduction and oxidation, respectively. Plasmonic photocatalysis, which uses noble metal nanoparticles (e.g., Au, Ag, Pt) deposited on semiconductor surfaces to enhance light absorption through localized surface plasmon resonance, is another active area. The plasmonic effect can generate hot electrons that are injected into the semiconductor, extending the spectral response into the visible and near-infrared regions. Additionally, upconversion nanoparticles that convert near-infrared light to visible or UV light can be integrated with conventional photocatalysts to utilize a broader portion of the solar spectrum.

Electrocatalytic and Advanced Oxidation Processes

Electrocatalytic water treatment uses an applied electric current to drive oxidation and reduction reactions at the surface of specially designed electrodes. The most common configuration is an electrochemical cell with two electrodes: an anode where oxidation of pollutants occurs directly or via electrogenerated oxidants, and a cathode where reduction reactions, such as hydrogen evolution or oxygen reduction to hydrogen peroxide, can take place. The choice of electrode material is decisive for efficiency, selectivity, and longevity. Noble metals like platinum and iridium offer high catalytic activity but are expensive and scarce. Boron-doped diamond (BDD) electrodes have emerged as a gold standard for anodic oxidation because of their wide electrochemical window, high oxygen evolution overpotential, chemical inertness, and ability to generate large quantities of hydroxyl radicals. BDD anodes can achieve nearly complete mineralization of organic pollutants, including recalcitrant compounds like phenol, chlorophenols, and pharmaceutical residues. However, the cost of BDD production is high, limiting its use to niche applications.

Mixed metal oxide (MMO) electrodes, such as Ti/IrO2-Ta2O5 and Ti/RuO2-IrO2, offer a more economical alternative with good stability and chlorine evolution activity, making them suitable for treating saline wastewater or producing active chlorine species for indirect oxidation. Recently, substoichiometric titanium dioxide (Ti4O7, known as Ebonex) and Magnéli phase titanium oxides have gained attention due to their high conductivity, corrosion resistance, and ability to generate hydroxyl radicals at moderate potentials. Three-dimensional porous electrodes, including carbon felt, graphite felt, and reticulated vitreous carbon, provide high surface area and enhanced mass transfer for both anodic oxidation and cathodic generation of hydrogen peroxide. When hydrogen peroxide is produced at the cathode in the presence of ferrous ions (Fe2+), the classical Fenton reaction occurs, producing hydroxyl radicals. This electrochemical Fenton process can be operated at circumneutral pH if heterogeneous catalysts (e.g., iron-loaded zeolites or iron minerals) are used instead of dissolved iron.

The integration of electrocatalysis with other advanced oxidation techniques offers synergistic benefits. Photoelectron-Fenton (PEF) processes combine anodic oxidation, cathodic H2O2 generation, and UV/visible light irradiation to accelerate the reduction of Fe3+ to Fe2+ and drive photoreduction of intermediates. Solar photoelectron-Fenton (SPEF) replaces UV lamps with solar irradiation, reducing energy costs. Another hybrid technology, sono-electrocatalysis, uses ultrasonic waves to enhance mass transfer and generate additional radical species through cavitation. The combination of electrocatalysis and membrane filtration, known as electrocatalytic membrane reactors (ECMRs), uses conductive membranes as both the filter and the electrode, enabling simultaneous separation and degradation of pollutants. This approach can reduce fouling and achieve high removal efficiencies for contaminants such as dyes, humic acids, and antibiotics.

One of the most exciting developments in electrocatalysis is the use of single-atom catalysts (SACs), where isolated metal atoms are dispersed on a conductive support such as nitrogen-doped carbon or graphene. SACs achieve maximal atom utilization and often exhibit distinct electronic properties that differ from their bulk or nanoparticle counterparts. For example, Fe-N-C catalysts (iron single atoms coordinated with nitrogen on a carbon matrix) have demonstrated outstanding activity for the oxygen reduction reaction to produce H2O2, which is crucial for in-situ generation of hydroxyl radicals. Co-N-C and Mn-N-C systems are also under investigation. The selectivity and activity of SACs can be tuned by adjusting the coordination environment, the type of metal center, and the properties of the support.

Despite these advances, several challenges remain for electrocatalytic water treatment. The most significant are the high cost of electrode materials, the need for stable and conductive supports, the formation of chlorinated byproducts when treating chloride-containing waters, and the energy consumption associated with large-scale applications. Researchers are addressing these issues through the development of earth-abundant electrode materials, optimized reactor geometries that reduce ohmic losses, and pulsed electrolysis strategies that modulate the electrode potential to minimize side reactions. Life-cycle assessment and techno-economic analysis are increasingly being used to evaluate the feasibility of electrocatalytic processes compared to conventional treatment methods.

Nanotechnology and Catalyst Design

Nanotechnology has provided the tools to engineer catalysts at the molecular level, enabling unprecedented control over size, shape, composition, surface structure, and porosity. The high surface-to-volume ratio of nanomaterials exposes a large fraction of atoms at active sites, dramatically increasing the number of reaction centers per unit mass. Moreover, nanoscale dimensions can alter electronic properties, such as band gap and charge carrier mobility, due to quantum confinement effects. This tunability allows researchers to optimize catalysts for specific reactions and operating conditions.

Among the most widely studied nanomaterials for catalysis are metal oxide nanoparticles, carbon-based nanostructures (including carbon nanotubes, graphene, and carbon dots), layered double hydroxides, MXenes, and two-dimensional transition metal dichalcogenides such as MoS2 and WS2. These materials can be synthesized via a variety of bottom-up and top-down approaches, including sol-gel processing, hydrothermal/solvothermal reactions, chemical vapor deposition, electrochemical exfoliation, and template-assisted methods. The choice of synthesis method affects not only the particle size and morphology but also the phase, crystallinity, defect density, and surface termination, all of which influence catalytic performance.

A key challenge in nanocatalyst design is aggregation: nanoparticles tend to agglomerate to reduce their high surface energy, which diminishes the number of accessible active sites and reduces catalytic activity. To overcome this, researchers immobilize nanoparticles on stable supports such as ceramics, polymers, mesoporous silica, or activated carbon. The support can also participate in the catalytic process by providing additional active sites, improving charge transfer, or stabilizing reactive intermediates. Core-shell structures, where a functional core is coated with a protective or functional shell, can also prevent aggregation while adding new functionalities. For example, Fe3O4@SiO2@TiO2 core-shell nanoparticles combine magnetic separability with photocatalytic activity, facilitating catalyst recovery and reuse.

Doping and defect engineering are powerful strategies for enhancing the intrinsic activity of nanocatalysts. Introducing oxygen vacancies in metal oxide catalysts, for instance, can create mid-gap states that enhance visible-light absorption and provide active sites for adsorption and activation of water, oxygen, and pollutants. Similarly, heteroatom doping into carbon frameworks (e.g., nitrogen, boron, phosphorus, or sulfur) can modulate the electronic structure of carbon atoms, creating charged sites that facilitate redox reactions. Defect-rich materials often exhibit superior catalytic performance compared to their pristine counterparts, as demonstrated by the high activity of defect-rich MoS2 for hydrodesulfurization and hydrogen evolution. In the context of water treatment, defect-rich TiO2 with oxygen vacancies has shown enhanced photocatalytic degradation of organic dyes and phenolic compounds.

Metal-organic frameworks (MOFs) represent a particularly versatile class of porous crystalline materials for catalytic water treatment. MOFs consist of metal nodes connected by organic linkers, yielding ultrahigh surface areas (up to 10,000 m2/g) and tunable pore sizes. The metal nodes can serve as active catalytic centers, while the organic linkers can be functionalized with specific groups to adsorb target pollutants. MOFs can also be used as precursors or templates for deriving highly porous carbon or metal oxide catalysts with controlled nanostructures. For example, zeolitic imidazolate framework-8 (ZIF-8) can be carbonized to produce nitrogen-doped porous carbons with excellent electrocatalytic activity. However, the stability of many MOFs in aqueous environments, particularly at extreme pH or in the presence of competing ions, remains a concern and is an active area of research.

The concept of tandem catalysis is gaining traction in nanocatalyst design for water treatment. In a tandem system, two or more catalytic functions are integrated into a single material, allowing sequential reactions to occur in close proximity. For instance, a nanocomposite that couples a photocatalyst with an enzyme or a metal nanoparticle can carry out both pollutant degradation and subsequent mineralization of intermediate products. This approach can avoid the accumulation of toxic intermediates and improve overall efficiency. Another exciting direction is the design of intelligent catalysts that respond to environmental stimuli such as pH, temperature, or the presence of specific pollutants, enabling on-demand activation and self-regulating performance.

Sustainable and Cost-Effective Solutions

For next-generation catalytic water treatment technologies to achieve real-world impact, they must be not only effective but also sustainable and economically viable. Sustainability considerations span the entire life cycle of the catalyst: the abundance and environmental impact of raw materials, the energy and resource footprint of synthesis, the operational energy demand, the fate of spent catalysts, and the potential for recycling and regeneration. The most promising catalysts are those based on earth-abundant elements such as iron, copper, manganese, titanium, and carbon, rather than scarce noble metals like platinum, palladium, ruthenium, or gold. Although noble metal catalysts often exhibit superior activity, their high cost and geopolitical supply risks make them unsuitable for large-scale water treatment, especially in low- and middle-income countries where the need for affordable clean water is greatest.

Solar-driven photocatalysis is attractive because it harnesses abundant, free, and renewable solar energy, eliminating the energy costs and carbon emissions associated with electrically powered systems. Even moderate solar-powered systems can achieve significant pollutant removal, especially in sun-rich regions. The development of photocatalysts that absorb visible and near-infrared light has been a priority because these wavelengths constitute the majority of the solar spectrum. The integration of photocatalysis with solar thermal or solar desalination systems could further reduce energy costs and improve overall water treatment efficiency. In addition, the use of non-toxic, biodegradable materials for catalyst supports and reactor components can minimize the environmental burden at the end of the system's life.

Catalyst stability and reusability are critical for both environmental and economic sustainability. A catalyst that can be reused for hundreds of cycles without significant loss of activity will have a much lower cost per volume of water treated than a single-use or short-lifetime material. Regeneration methods, such as washing with mild acid or base, thermal annealing, or UV irradiation to remove adsorbed foulants, can restore activity and extend catalyst life. Immobilization on magnetic supports enables easy recovery using an external magnetic field, avoiding the need for centrifugation or filtration. The development of self-cleaning catalyst surfaces that resist fouling by organic matter or biofilms is an active research area, drawing inspiration from natural phenomena such as the lotus leaf.

Techno-economic analysis (TEA) and life-cycle assessment (LCA) are essential tools for comparing emerging catalytic technologies with established methods. A comprehensive TEA accounts for capital costs (reactor, electrodes, pumps, controls), operating costs (electricity, chemicals, labor, maintenance), catalyst replacement costs, and the value of treated water. LCA evaluates the environmental impacts across all stages, including greenhouse gas emissions, resource depletion, ecotoxicity, and water footprint. For example, a recent LCA of TiO2 photocatalytic treatment of pharmaceutical wastewater found that while the process achieves high removal efficiencies, the energy required for UV lamps can contribute significantly to the carbon footprint unless solar irradiation is used. Similarly, the production of some advanced nanomaterials may involve toxic solvents or high-temperature processes that offset some of the environmental benefits gained during operation. These analyses help guide research priorities toward the most sustainable combinations of materials and processes.

Government policies and regulatory frameworks also play a role in the adoption of catalytic water treatment technologies. Stricter discharge standards for emerging contaminants, such as the European Union's recent limits on PFAS in drinking water, create incentives for utilities and industries to invest in advanced treatment processes. Green public procurement programs can favor technologies that use renewable energy and non-toxic materials. International partnerships and technology transfer initiatives can help deploy catalytic water treatment in developing regions where water quality challenges are most acute. The United Nations Sustainable Development Goal 6, which calls for universal access to safe and affordable drinking water, provides a global framework for action.

Future Perspectives and Challenges

Despite the remarkable progress in catalytic water treatment, the path from laboratory discovery to commercial deployment is long and uncertain. Several fundamental challenges must be addressed to bridge the gap between research and practice. First, the stability and longevity of catalysts under realistic operating conditions remain insufficient for many promising materials. Real wastewater contains complex mixtures of pollutants, natural organic matter, inorganic ions, suspended solids, and variable pH, all of which can deactivate catalysts through fouling, poisoning, dissolution, or structural transformation. Long-term field trials with real wastewater matrices are essential to validate laboratory findings and identify failure modes.

Second, the selectivity of catalytic processes needs improvement. Most advanced oxidation processes produce hydroxyl radicals, which are non-selective and can react with non-target species such as natural organic matter, inorganic anions, and intracellular biomolecules, consuming oxidant capacity and potentially generating harmful byproducts. For example, in chloride-rich waters, hydroxyl radicals can be scavenged by chloride ions to form chlorine radicals, which can then form chlorinated organic compounds. Selective catalysis, where the catalyst preferentially adsorbs and degrades target pollutants without interference from background constituents, is an important goal. Molecularly imprinted polymers (MIPs) and shape-selective catalysts with tailored pore architecture can provide the necessary selectivity, but integrating them with catalytic functionality is non-trivial.

Third, scalability and cost remain major barriers. While laboratory experiments often use high catalyst loadings, well-defined light sources, and pure water, real applications require handling large volumes of water with fluctuating quality and flow rates. Reactor design must be optimized for uniform light distribution in photocatalytic systems, efficient mass transfer in electrocatalytic cells, and low pressure drop in fixed-bed reactors. Scale-up studies typically follow a progression from batch to continuous flow, from bench-scale to pilot-scale, and finally to full-scale demonstration. The involvement of chemical engineers, process economists, and water utility operators at an early stage can accelerate this transition.

Fourth, the assessment of treatment efficacy must go beyond the removal of parent pollutants to evaluate toxicity, biodegradability, and the formation of transformation products. Partial degradation of a pollutant can sometimes produce intermediates that are more toxic or persistent than the original compound. For instance, the photocatalytic degradation of some antibiotics can yield intermediates that retain antibacterial activity or promote antibiotic resistance. Bioassays using indicator organisms such as Daphnia magna, Vibrio fischeri (Microtox), or human cell lines provide a more comprehensive measure of ecotoxicity and health risk. Analytical tools such as non-targeted high-resolution mass spectrometry are increasingly used to identify transformation products and elucidate degradation pathways.

Finally, the integration of catalytic processes into existing water treatment infrastructure requires careful consideration of hydraulic compatibility, operational complexity, and maintenance requirements. Retrofitting a conventional treatment plant with a photocatalytic system, for example, may require additional space for reactors, changes in piping and pumping, and training for operators. Modular and containerized systems offer a flexible alternative, particularly for decentralized applications such as remote communities, humanitarian relief camps, or industrial wastewater pre-treatment. The energy source is also a critical factor: solar-driven systems are best suited to sunny climates with adequate land area, while electrocatalytic systems may be more appropriate where grid electricity is reliable and cheap.

Looking ahead, several emerging trends are likely to shape the next decade of catalytic water treatment research. Artificial intelligence and machine learning are being applied to accelerate catalyst discovery by predicting composition-activity relationships from large datasets of experimental and computational data. High-throughput experimentation, robotics, and automated synthesis platforms enable the rapid screening of thousands of catalyst candidates. The concept of digital twins, where a real-time digital replica of a treatment system is used for process optimization and predictive maintenance, is also gaining interest. The convergence of catalysis with other advanced technologies such as nanotechnology, biotechnology, sensing, and control systems could lead to smart water treatment systems that autonomously adapt to changing water quality conditions, optimize energy consumption, and self-diagnose failures.

Collaboration across disciplines and sectors will be essential to realize the potential of catalytic water treatment. Chemists, materials scientists, engineers, environmental health experts, economists, and policymakers must work together to define research priorities, evaluate trade-offs, and design demonstration projects. Funding agencies and international organizations can support this collaboration by establishing multi-institutional consortia, funding pilot-scale research, and sharing best practices. With sustained investment and innovation, next-generation catalytic processes can play a major role in achieving universal access to clean water and protecting ecosystems from chemical pollution.

Conclusions

Next-generation catalytic processes represent a paradigm shift in water treatment, moving from physical separation toward chemical transformation of contaminants into harmless products. Photocatalysis, electrocatalysis, and hybrid advanced oxidation processes offer the potential to degrade a wide range of persistent pollutants, including pharmaceuticals, PFAS, pesticides, and industrial dyes, under mild conditions with renewable energy. The rational design of nanostructured catalysts, with controlled size, morphology, composition, and surface chemistry, has dramatically improved activity, selectivity, and stability. The use of earth-abundant elements, sustainable synthesis routes, and solar energy aligns catalytic water treatment with the principles of green chemistry and circular economy.

However, significant challenges remain in scaling these technologies from the bench to the field. Catalyst stability in real water matrices, selectivity for target pollutants, reactor design and hydrodynamics, energy efficiency, and economic competitiveness all require further development and demonstration. The integration of catalytic processes into existing infrastructure, as well as the development of modular and decentralized systems, will be crucial for broad adoption. The convergence of catalysis with digital tools, such as AI-driven discovery, machine learning optimization, and smart process control, holds promise for accelerating progress. With the right investments in research, development, and deployment, catalytic water treatment can become a cornerstone of global efforts to provide safe, affordable, and sustainable water for all.

  • Development of visible-light-active photocatalysts such as N-doped TiO2, BiVO4, and g-C3N4 for solar-driven pollutant degradation
  • Design of durable, recyclable nanocatalysts with controlled morphology and core-shell architectures for enhanced stability
  • Integration of electrocatalytic oxidation with membrane filtration and Fenton processes for synergistic treatment
  • Exploration of single-atom catalysts and defect-engineered materials for selective and efficient contaminant removal
  • Utilizing renewable energy sources such as solar and low-voltage electricity for sustainable operation
  • Deployment of techno-economic analysis and life-cycle assessment to guide development toward cost-effective and environmentally benign solutions
  • Advancement of reactor designs including compound parabolic collectors, electrochemical flow cells, and electrocatalytic membrane reactors for practical scale-up
  • Collaboration between researchers, engineers, policymakers, and water utilities to translate laboratory innovations into real-world water treatment systems

For further reading on photocatalytic water treatment, see the comprehensive review in Physical Chemistry Chemical Physics and the open-access article on emerging photocatalysts in npj Clean Water. Recent advances in electrocatalytic advanced oxidation processes are detailed in Environmental Science & Technology. For sustainability and economic perspectives, refer to the life-cycle assessment of photocatalytic systems in Desalination. The role of single-atom catalysts in water treatment is discussed in a recent review in Advanced Materials.