Tuning electronic structure of metal-free dual-site catalyst enables exclusive singlet oxygen production and in-situ utilization.

Developing eco-friendly catalysts for effective water purification with minimal oxidant use is imperative. Herein, we present a metal-free and nitrogen/fluorine dual-site catalyst, enhancing the selectivity and utilization of singlet oxygen (1O2) for water decontamination. Advanced theoretical simulations reveal that synergistic fluorine-nitrogen interactions modulate electron distribution and polarization, creating asymmetric surface electron configurations and electron-deficient nitrogen vacancies. These properties trigger the selective generation of 1O2 from peroxymonosulfate (PMS) and improve the utilization of neighboring reactive oxygen species, facilitated by contaminant enrichment at the fluorine-carbon Lewis-acid adsorption sites. Utilizing these insights, we synthesize the catalyst through montmorillonite (MMT)-assisted pyrolysis (NFC/M). This method leverages the role of MMT as an in-situ layer-stacked template, enabling controlled decomposition of carbon, nitrogen, and fluorine precursors and resulting in a catalyst with enhanced structural adaptability, reactive site accessibility, and mass-transfer capacity. The NFC/M demonstrates an impressive 290.5-fold increase in phenol degradation efficiency than the single-site analogs, outperforming most of metal-based catalysts. This work not only underscores the potential of precise electronic and structural manipulations in catalyst design but also advances the development of efficient and sustainable solutions for water purification.

Humic substances mediated superior photochemical pollutant conversion on defective TiO2 in environmentally relevant matrices: The key roles of oxygen vacancy in surface interactions, oxidant activation and radical generation.

Ubiquitous humic substances usually exhibit strong interfering effects on target pollutant removal in advanced water purification. This work aims to develop a photochemical conversion system on the nonstoichiometric TiO2 for pollutant removal in environmentally relevant matrices. In this synergistic reaction system, the redox-reactive humic substances and defective oxygen vacancies can serve as the organic electron transfer mediator and the key surface reactive sites, respectively. This system achieves a superior pollutant degradation in real surface water at low oxidant concentrations. Reactive oxygen vacancies on the TiO2 surface and sub-surface are of considerable interest for this photochemical reaction system. By engineering defective oxygen vacancies on high-energy {001} polar facet, the surface and electronic interactions between tailored TiO2 and humic substances are greatly strengthened for the promoted electron transfer and oxidant activation. Rendered by the strong surface affinity and molecular activation, defective oxygen vacancies thermodynamically and dynamically promote reactive chain reactions for free radical formation, including the selective O2 reduction to ·O2- and the H2O2 activation to ·OH. Our findings take new insights into environmental geochemistry, and provide an effective strategy to in-situ boost the humic substances-mediated water purification without secondary pollution. ENVIRONMENTAL IMPLICATION: Humic substances are widely distributed in aquatic environment, thus playing important roles in environmental geochemistry. For example, humic substances can achieve good surface adsorption through electrostatic adsorption, ligand exchange and electronic interactions with typical TiO2 to form reactive ligand-metal charge transfer complexes for pollutant degradation. Inspired by the unique properties of surface and sub-surface oxygen vacancies, the defective TiO2 was designed to refine the humic substances-mediated photochemical reactions. A superior reactivity was measured for pollutant degradation. Our findings provide an effective strategy to boost naturally photochemical decontamination in environmentally relevant matrices.

Slow-release synthesis of Cu single-atom catalysts with the optimized geometric structure and density of state distribution for Fenton-like catalysis.

Single-atom Fenton-like catalysis has attracted significant attention, yet the quest for controllable synthesis of single-atom catalysts (SACs) with modulation of electron configuration is driven by the current disadvantages of poor activity, low selectivity, narrow pH range, and ambiguous structure-performance relationship. Herein, we devised an innovative strategy, the slow-release synthesis, to fabricate superior Cu SACs by facilitating the dynamic equilibrium between metal precursor supply and anchoring site formation. In this strategy, the dynamics of anchoring site formation, metal precursor release, and their binding reaction kinetics were regulated. Bolstered by harmoniously aligned dynamics, the selective and specific monatomic binding reactions were ensured to refine controllable SACs synthesis with well-defined structure-reactivity relationship. A copious quantity of monatomic dispersed metal became deposited on the C3N4/montmorillonite (MMT) interface and surface with accessible exposure due to the convenient mass transfer within ordered MMT. The slow-release effect facilitated the generation of targeted high-quality sites by equilibrating the supply and demand of the metal precursor and anchoring site and improved the utilization ratio of metal precursors. An excellent Fenton-like reactivity for contaminant degradation was achieved by the Cu1/C3N4/MMT with diminished toxic Cu liberation. Also, the selective ·OH-mediated reaction mechanism was elucidated. Our findings provide a strategy for regulating the intractable anchoring events and optimizing the microenvironment of the monatomic metal center to synthesize superior SACs.

Recycling chestnut shell for superior peroxymonosulfate activation in contaminants degradation via the synergistic radical/non-radical mechanisms.

The efficient recycling of agricultural chestnut shell waste is of considerable interest due to its large availability and economic feasibility. Herein, an alkaline-activated biochar was thermally prepared using chestnut shell by finely regulating main conditions; its morphological, structural and physic-chemical properties were well characterized. Fenton-like capacity to trigger peroxymonosulfate activation for superior pollutant degradation with high efficiency and good selectivity was validated in different water matrix. Both radical formation and electron transfer were identified as reaction pathways, while the selective non-radical mechanism played the major role in pollutant degradation. Surface ketonic groups were identified as the main reactive sites for non-selective radical production, while crystal edges and structural defects on sp2/sp3 carbon network could smoothly mediate the selective electron transfer from pollutant to oxidant in the non-radical Fenton-like catalysis. The two-mixed radical/non-radical pathways exhibited important advantages for environmental decontamination, in comparison with the one-single radical or non-radical mechanism. Our study provided a promising recycling strategy for agricultural chestnut shell, as well as an environment-friendly catalyst for heterogeneous Fenton-like catalysis in green water purification rendered by the synergistic radical/non-radical reaction pathways.

Superior degradation of phenolic contaminants in different water matrices via non-radical Fenton-like mechanism mediated by surface-disordered WO3.

Heterogeneous Fenton-like catalysis mediated by solid catalyst is a promising oxidation technology for water purification. The redox reactivity, cost-effectiveness, and environmental compatibility of solid catalyst play governing roles in oxidant activation, radical generation, and pollutant degradation. Herein, the surface-disordered WO3 (D-WO3) functionally engineered by the unique crystalline-amorphous core-shell structure is proven to be a superior solid catalyst of heterogeneous Fenton-like catalysis for peroxymonosulfate (PMS) activation and pollutant degradation in various water matrices. Six typical phenolic and dye pollutants are effectively and selectively degraded in the D-WO3/PMS system with much reduced matrix effects. Both radical identifying and scavenging tests elucidate the important role of non-radical 1O2 and mediated electron transfer during PMS activation on the D-WO3 surface. The superior Fenton-like activity of D-WO3 can be mainly attributed to the surface and sub-surface distorted lattice sites with finely tailored atomic and electronic structures and surface chemistry. These distorted lattice sites can thermodynamically serve as the key reactive centers of dissociative adsorption and catalytic activation for both PMS and pollutant, with high adsorption energy, strong structural activation, and smooth electron transfer. Our findings provide a new chance for heterogeneous Fenton-like catalysis mediated by transition metal oxides with high capacity, low cost, and no toxicity for promising water purification.

Reusing Sulfur-Poisoned Palladium Waste as a Highly Active, Nonradical Fenton-like Catalyst for Selective Degradation of Phenolic Pollutants.

Recycling of deactivated palladium (Pd)-based catalysts can not only lower the economic cost of their industrial use but also save the cost for waste disposal. Considering that the sulfur-poisoned Pd (PdxSy) with a strong Pd-S bond is difficult to regenerate, here, we propose a direct reuse of such waste materials as an efficient catalyst for decontamination via Fenton-like processes. Among the PdxSy materials with different poisoning degrees, Pd4S stood out as the most active catalyst for peroxymonosulfate activation, exhibiting pollutant-degradation performance rivaling the Pd and Co2+ benchmarks. Moreover, the incorporated S atom was found to tune the surface electrostatic potentials and charge densities of the Pd active site, triggering a shift in catalytic pathway from surface-bound radicals to predominantly direct electron transfer pathway that favors a highly selective oxidation of phenols. The catalyst stability was also improved due to the formation of strong Pd-S bond that reduces corrosion. Our work paves a new way for upcycling of Pd-based industrial wastes and for guiding the development of advanced oxidation technologies toward higher sustainability.

Degradation of aqueous methylparaben by non-thermal plasma combined with ZnFe2O4-rGO nanocomposites: Performance, multi-catalytic mechanism, influencing factors and degradation pathways.

Non-thermal plasma (NTP) combined with zinc ferrite-reduced graphene oxide (ZnFe2O4-rGO) nanocomposites were used for the degradation of aqueous methylparaben (MeP). ZnFe2O4-rGO nanocomposites were prepared using the hydrothermal method, with the structure and photoelectric properties of nanocomposites then characterized. The effects of discharge power, initial MeP concentration, initial pH, and air flow rate on MeP degradation efficiency were investigated, and the multi-catalytic mechanism and MeP degradation pathways were established. Results showed that ZnFe2O4-rGO nanocomposites with a 10%:90% mass ratio of GO:ZnFe2O4 had an optimal catalytic effect. The MeP degradation efficiency of NTP combined with ZnFe2O4-rGO (10 wt%), was approximately 25% higher than that of NTP alone. Conditions favorable for MeP degradation included higher discharge power, lower MeP concentration, neutral pH value, and higher air flow rate. The degradation of MeP by NTP combined with ZnFe2O4-rGO nanocomposites followed pseudo-first-order kinetics. O2•-, •OH, H2O2, and O3 were found to play important roles in the MeP degradation, as part of the multi-catalytic mechanism of NTP combined with ZnFe2O4-rGO nanocomposites. MeP degradation pathways were proposed based on the degradation intermediates detected by gas chromatography mass spectrometry, including demethylation, hydroxylation, carboxylation, ring-opening, and mineralization reactions. The prepared ZnFe2O4-rGO nanocomposites provide an approach for improved contaminant degradation efficiency, with reduced energy consumption in the NTP process.

In situ organic Fenton-like catalysis triggered by anodic polymeric intermediates for electrochemical water purification.

Organic Fenton-like catalysis has been recently developed for water purification, but redox-active compounds have to be ex situ added as oxidant activators, causing secondary pollution problem. Electrochemical oxidation is widely used for pollutant degradation, but suffers from severe electrode fouling caused by high-resistance polymeric intermediates. Herein, we develop an in situ organic Fenton-like catalysis by using the redox-active polymeric intermediates, e.g., benzoquinone, hydroquinone, and quinhydrone, generated in electrochemical pollutant oxidation as H2O2 activators. By taking phenol as a target pollutant, we demonstrate that the in situ organic Fenton-like catalysis not only improves pollutant degradation, but also refreshes working electrode with a better catalytic stability. Both 1O2 nonradical and ·OH radical are generated in the anodic phenol conversion in the in situ organic Fenton-like catalysis. Our findings might provide a new opportunity to develop a simple, efficient, and cost-effective strategy for electrochemical water purification.

Stable Electrochemical Determination of Dopamine by a Fluorine-Terminated {001}-Exposed TiO2 Single Crystal Sensor.

Photochemical oxidation is able to effectively regenerate the fouled electrode in electrochemical pollutant monitoring, while its regeneration capacity is limited by the surface-bound hydroxyl radical speciation with low activity and mobility, which is attributed to the dissociated water adsorption on hydrophilic metal oxides. In this work, fluorine-terminated {001}-exposed TiO2 single crystals (F-TiO2) are rationally designed to construct an Au-based electrochemical sensor (Au/F-TiO2) for dopamine (DA) detection in different matrices. The Au/F-TiO2 sensor exhibits an efficient and stable detection capacity in both environmental and biological samples. A superior photochemical regeneration capacity is obtained on the Au/F-TiO2 electrode with much reduced matrix effects under UV irradiation. Spectral observation, crystallographic analysis, pollutant degradation performance, radical inhibition, and surface enhanced Raman scattering tests reveal that both the fluorine-terminated surface chemical features and the bulk-free radical speciation are mainly responsible for the superior photochemical regeneration capacity of the Au/F-TiO2 electrode. Even for the real biological samples, a stable electrochemical DA detection is also achieved on the Au/F-TiO2 sensor. Our work establishes a new approach to refine electrochemical sensors for stable monitoring and provides a robust photoactive electrode substrate with high efficiency and low cost for practical applications.

Synergistic degradation of acid orange 7 dye by using non-thermal plasma and g-C3N4/TiO2: Performance, degradation pathways and catalytic mechanism.

In order to harness the full capability of ultraviolet and visible light in the dielectric barrier discharge induced non-thermal plasma (DBD-NTP) process, g-C3N4/TiO2 catalysts were prepared and utilized in this process. Synergistic degradation of acid orange 7 (AO7) dye by DBD-NTP and g-C3N4/TiO2 was conducted, and the performance, degradation pathways and synergistic catalytic mechanism were investigated. The results showed that the degradation rate of AO7 in the DBD-NTP and g-C3N4-15/TiO2 process increased by 39.1% compared with that in the single DBD-NTP process at 12 min discharge time. At 20 W input power, initial concentration of AO7 was 5 mg/L, catalytic dosage was 0.5 g/L, initial pH value was 10.0 and air flow rate was 52 L/h, the degradation rate of AO7 reached 100.0% after 12 min discharge time. Higher discharge power and initial concentration of AO7 inhibited AO7 degradation, whereas increasing the air flow rate and initial pH value of the solution promoted AO7 degradation. The degradation pathways of AO7 consisted of azo structure destruction, ring opening reaction, hydroxylation, carboxylation and mineralization reaction. The results of radical trapping experiment showed that O2-, h+, OH, O3 and H2O2 were the main reactive species for AO7 degradation in the DBD-NTP and g-C3N4-15/TiO2 process. The Z-scheme photocatalytic mechanism for the g-C3N4/TiO2 catalyst was proposed.

Photochemical pollutant degradation on facet junction-engineered TiO2 promoted by organic arsenical: Governing roles of arsenic-terminated surface chemistry and bulk-free radical speciation.

Photochemical oxidation based on semiconducting metal oxides is an efficient strategy to remove environmental pollutants in water, air and soil. The fine manipulation of photo-carriers separation, surface chemistry and radical speciation is of considerable interest for environmental remediation. In this work, the morphology- and structure-tailored TiO2 single crystals with epitaxial {101}/{001} facet junction were designed, prepared and tested for photochemical pollutant oxidation in the presence of organic arsenicals, the main component in swine wastewater from livestock industry, although they have been forbidden for several years. The facet junction-tailored TiO2 deserved an efficient photo-carriers separation with high quantum efficiency. The photochemical oxidation of 4-chlorophenol (4-CP), phenol and bisphenol A (BPA) was substantially improved by roxarsone (ROX). ROX-enhanced photochemical activity of TiO2 was mainly attributed to the in-situ arsenic-terminated surface chemistry by Ti-OAsVO3/-OAsIIIO2. This surface played governing roles in water/TiO2 interactions, and changed water adsorption from dissociative to molecular configuration. Furthermore, ·OH was finely regulated from low-activity surface-bound to high-activity bulk-free speciation between as-generated photo-holes with free water molecules. Our findings provided a new chance to refine the TiO2-based photochemical oxidation, and a modifying technology to treat swine wastewater from livestock industry with much reduced secondary pollution.

Non-radical activation of H2O2 by surface-disordered WO3 for efficient and selective pollutant degradation with weak matrix effects.

Heterogeneous catalysis is promising for water treatment. Solid catalysts play governing roles. Herein, the surface-disordered WO3, D-WO3, engineered with surface and sub-surface defective sites from NaBH4 reduction was proven to be an effective catalyst for H2O2 activation. The defective degree and defects amount on WO3 were regulated by NaBH4. More than 95% of two typical azo dyes, RhB and MG, were selectively degraded in D-WO3/H2O2 system during 3.0 h, while no significant activity was observed for MO as well as bisphenol A, roxarsone, phenol, 4-chlorophenol, p-nitrophenol, o-aminophenol, urea, and 2,4-dichlorophenol in comparison under the identical conditions (mainly less than 20%). Both ESR and radical scavenging tests indicated the minor role of ·OH from H2O2 activation on D-WO3. The superior activity of D-WO3 could be mainly attributed to the surface and sub-surface defects with finely tailored local atomic configurations and electronic structures of central metal sites. Surface and sub-surface defective sites could serve as the reactive sites of interfacial adsorption, dissociative activation, and catalytic decomposition for both oxidant and pollutants, with high adsorption energy, strong structural activation, and superior catalytic activity. Our findings provided a new chance for non-selective radical catalysis based on transition metal oxides and a promising catalyst with high performance, low cost, and no toxicity for pollutant degradation with weak matrix effects in wastewater and surface water.

Electrochemical treatment of phenol-containing wastewater by facet-tailored TiO2: Efficiency, characteristics and mechanisms.

Electrochemical oxidation is widely used for water and wastewater treatment. Anodic material is crucial and the shape-tailored {001}-exposed TiO2 has been proven to be an ideal electrode material for pollutant oxidation. In this work, the electrochemical treatment of wastewater containing typical p-substituted phenols by facet-tailored TiO2 is studied in terms of efficiency, characteristics and mechanisms. Experimental results demonstrate that the anodic oxidation of p-substituted phenols becomes more difficult with the increasing Hammett's constant (σ) of phenols, while their degradation rates (k) increase continuously with the initial surface concentration (Γ). Phenols are degraded mainly by surface-bound ·OH and direct electron transfer on the TiO2/Ti electrode, rather than by bulk-free ·OH suspended in the aqueous phase. Theoretical calculations reveal that the surface-bound ·OH-mediated oxidation mechanism is attributed mainly to the strong surface bond strength between shape-tailored TiO2 and water molecule as well as the reactive ·OH. Such strong interactions are associated with the higher density of atomic steps, edges and kinks of low-coordinate surface atoms with a large number dangling bonds on the high-energy {001} polar facet. For practical treatment of real wastewater with different matrixes, the facet-tailored TiO2/Ti electrode exhibits both a high efficiency and a fast kinetics. Our findings provide a new chance to degrade phenolic pollutants in wastewater and offer atomic-scale insights into the preparation, modification and application of TiO2-based anodic materials for electrochemical water treatment.

Photochemical Protection of Reactive Sites on Defective TiO2- x Surface for Electrochemical Water Treatment.

The electrode is the key in electrochemical process for water and wastewater treatment. Many nonstoichiometric metal oxides are active electrode materials but have poor stability under strong anodic polarization due to their susceptible nature of the oxygen vacancies on surface and subsurface as defective reactive sites. In this work, a novel photochemical protecting strategy is proposed to stabilize the defective reactive sites on the TiO2- x surface and subsurface for long-term anodic oxidation of pollutants. With this strategy, a novel photoassisted electrochemical system at low anodic bias is further constructed. Such a system exhibits a high protecting capacity at a low operation cost for electrochemical degradation of bisphenol A (BPA), a typical persistent organic pollutant. Its excellent photochemical protecting capacity is found to be mainly attributed to the mild non-band-gap excitation pathways on the defective TiO2- x electrode under both visible-light irradiation and moderate anodic polarization. Under real sunlight irradiation, a 20 run cyclic test for BPA degradation demonstrates the excellent performance and stability of the constructed system at low bias without significant oxygen evolution. Our work provides a new opportunity to utilize the defective and reactive TiO2- x for efficient, stable, and cost-effective electrochemical water treatment with the aid of its photo- and electrochemical bifunctional properties.

Photo-assisted electrochemical detection of bisphenol A in water samples by renewable {001}-exposed TiO2 single crystals.

Bisphenol A (BPA) is a semi-persistent environmental endocrine disrupter and widely present in aqueous environments. Electrochemical detection is an effective method to monitor pollutants like BPA in aqueous environments. However, the electrode fouling from anodic polymeric products is one main barrier of electrochemical sensors for their practical applications. In this work, a renewable electrochemical sensor was rationally designed, constructed and tested for efficient BPA detection. The TiO2 anodic material was surface-engineered by inorganic-framework molecular imprinting sites with tailored morphological shape, exposed facet and crystal structure. This electrode could be activated mainly as an electrochemical catalyst and partially as a photochemical catalyst. The developed TiO2-based sensor exhibited a good detection reliability and cyclic stability for determining BPA in water samples, with an electrochemical signal decrease of less than 5.0% in 10-run cyclic tests. By virtue of the bi-functional properties of the tailored TiO2 anodic material, a unique photo-assisted electrochemical sensor was further developed, in which analyte digestion and analytical signal originated mainly from anodic conversion. Such a synergistic digesting mechanism distinguishes it from the reported electro-assisted photochemical TiO2 sensors. Our work provides a robust sensor for monitoring pollutants in aqueous environments and a new opportunity to develop renewable electrode materials with good reusability.

Adsorption of phosphorus by using magnetic Mg-Al-, Zn-Al- and Mg-Fe-layered double hydroxides: comparison studies and adsorption mechanism.

Mg-Al, Zn-Al and Mg-Fe magnetic layered double hydroxide (LDH) adsorbents were synthesized. The adsorption effect and influencing factors of these adsorbents were explored, and the adsorption mechanism of phosphorus was studied with advanced instruments. The results showed that the best adsorption performance was observed when the molar ratio of metals was 3 for the magnetic LDH adsorbents, and the maximum adsorption amount for phosphorus was 74.8, 80.8 and 67.8 mg/g for Mg-Al, Zn-Al and Mg-Fe LDHs, respectively. Pseudo-second-order kinetics could be used to describe the adsorption process of phosphorus onto the magnetic LDHs. The adsorption of phosphorus onto the magnetic LDHs was an exothermic process. Lower temperatures were favourable for adsorption, and the adsorption of phosphorus onto the magnetic LDHs was a spontaneous process. When the solid-liquid ratios were 0.10 g/L, 0.10 g/L and 0.05 g/L for Mg-Al, Zn-Al and Mg-Fe magnetic LDHs, respectively, the highest adsorption amount of phosphorus was achieved for each magnetic LDH. The maximum adsorption amount was observed at pH values of 6.0-8.0. The inhibitory effect of HCO3- on the adsorption capacity of phosphorus onto the magnetic LDHs was the strongest at a higher HCO3- concentration level. The relative content of -OH significantly reduced after adsorption of phosphorus by the FTIR analysis, which indicated that the mechanism of phosphorus removal was mainly through the exchange between hydroxyl on the adsorbent surface and phosphorus in water. XPS studies showed that oxygen provided electrons during the adsorption of phosphorus.

Electrochemical Sensing of Bisphenol A on Facet-Tailored TiO2 Single Crystals Engineered by Inorganic-Framework Molecular Imprinting Sites.

Noble metals, nanostructured carbon, and their hybrids are widely used for electrochemical detection of persistent organic pollutants. However, despite of the rapid detection process and high accuracy, these materials generally suffer from high costs, metallic impurity, heterogeneity, irreversible adsorption and poor sensitivity. Herein, the high-energy {001}-exposed TiO2 single crystals with specific inorganic-framework molecular recognition ability was prepared as the electrode material to detect bisphenol A (BPA), a typical and widely present organic pollutant in the environment. The oxidation peak current was linearly correlated to the BPA concentration from 10.0 nM to 20.0 µM ( R2 = 0.9987), with a low detection limit of 3.0 nM (S/N = 3). Furthermore, it exhibited excellent discriminating ability, high anti-interference capacity, and good long-term stability. Its good performance for BPA detection in real environmental samples, including tap water, lake and river waters, domestic wastewater, and municipal sludge, was also demonstrated. This work extends the applications of TiO2 semiconductor and suggests that this material could be used as a highly active, stable, low-cost, and environmentally benign electrode material for electrochemical sensing.

Photochemical Anti-Fouling Approach for Electrochemical Pollutant Degradation on Facet-Tailored TiO2 Single Crystals.

Electrochemical degradation of refractory pollutants at low bias before oxygen evolution exhibits high current efficiency and low energy consumption, but its severe electrode fouling largely limits practical applications. In this work, a new antifouling strategy was developed and validated for electrochemical pollutant degradation by photochemical oxidation on facet-tailored {001}-exposed TiO2 single crystals. Electrode fouling from anodic polymers at a low bias was greatly relieved by the free ·OH-mediated photocatalysis under UV irradiation, thus efficient and stable degradation of bisphenol A, a typical environmental endocrine disrupter, and treatment of landfill leachate were accomplished without remarkable oxygen evolution in synergistic photoassisted electrochemical system. Electrochemical and spectroscopic measurements indicated a clean electrode surface during cyclic pollutant degradation. Such a photochemical antifouling strategy for low-bias anodic pollutants degradation was mainly attributed to the improved electric conductivity and excellent electrochemical and photochemical activities of tailored TiO2 anodic material, whose unique properties originated from the favorable surface atomic and electronic structures of high-energy {001} polar facet and single-crystalline structure. Our work opens up a brand new approach to develop catalytic systems for efficient degradation of refractory contaminants in water and wastewater.

A simple strategy to refine Cu2O photocatalytic capacity for refractory pollutants removal: Roles of oxygen reduction and Fe(II) chemistry.

Visible-light-driven photocatalysis is a promising technology for advanced water treatment, but it usually exhibits a low efficiency. Cu2O is a low-cost semiconductor with narrow band gap, high absorption coefficient and suitable conduction band, but suffers from low charge mobility, poor quantum yield and weak catalytic performance. Herein, the Cu2O catalytic capacity for refractory pollutants degradation is drastically improved by a simple and effective strategy. By virtue of the synergistic effects between photocatalysis and Fenton, a novel and efficient photocatalysis-driven Fenton system, PFC, is originally proposed and experimentally validated using Cu2O/Nano-C hybrids. The synergistic PFC is highly Nano-C-dependent and exhibits a significant superiority for the removal of rhodamine B and p-nitrophenol, two typical refractory pollutants in wastewater. The PFC superiority is mainly attributed to: (1) the rapid photo-electron transfer driven by Schottky-like junction, (2) the selective O2 reduction mediated by semi-metallic Nano-C for efficient H2O2 generation, (3) the specific H2O2 activation and large OH generation catalyzed by Haber-Weiss Fenton mechanism, and (4) the accelerated Fe2+/Fe3+ cycling and robust Fe2+ regeneration via two additional pathways. Our findings might provide a new chance to overcome the intrinsic challenges of both photocatalysis and Fenton, as well as develop novel technology for advanced water treatment.

Efficient Electrochemical Reduction of Nitrobenzene by Defect-Engineered TiO2-x Single Crystals.

TiO2 is a typical semiconductor and has been extensively used as an effective photocatalyst for environmental pollution control. But it could not be used as an electrochemical reductive catalyst because of its low electric conductivity and electrocatalytic activity. In this work, however, we demonstrate that TiO2 can act as an excellent cathodic electrocatalyst when its crystal shape, exposed facet and oxygen-stoichiometry are finely tailored by the local geometric and electronic structures. The defect-engineered TiO2-x single crystals dominantly exposed by high-energy {001} facets exhibits a high cathodic activity and great stability for electrochemical reduction of nitrobenzene, a typical refractory pollutant with high toxicity in environment. The single crystalline structure, the high-energy {001} facet and the defective oxygen vacancy of the defect-engineered TiO2-x single crystals are found to be mainly responsible for their cathodic superiority. With the findings in this work, a more practical non-Pd cathodic electrocatalyst could be prepared and applied for electrocatalytic reduction of refractory pollutants in water and wastewater, and extend the promising applications of TiO2 in the fields of environmental science.