Solar-assisted selective separation and recovery of precious group metals from deactivated air purification catalysts.

The mitigation of environmental and energy crises could be advanced by reclaiming platinum group precious metals (PGMs) from decommissioned air purification catalysts. However, the complexity of catalyst composition and the high chemical inertness of PGMs significantly impede this process. Consequently, recovering PGMs from used industrial catalysts is crucial and challenging. This study delves into an environmentally friendly approach to selectively recover PGMs from commercial air purifiers using photocatalytic redox technology. Our investigation focuses on devising a comprehensive strategy for treating three-way catalysts employed in automotive exhaust treatment. By meticulously pretreating and modifying reaction conditions, we achieved noteworthy results, completely dissolving and separating rhodium (Rh), palladium (Pd), and platinum (Pt) within a 12-h time frame. Importantly, the solubility selectivity persists despite the remarkably similar physicochemical properties of Rh, Pd, and Pt. To bolster the environmental sustainability of our method, we harness sunlight as the energy source to activate the photocatalysts, facilitating the complete dissolution of precious metals under natural light irradiation. This eco-friendly recovery approach demonstrated on commercial air purifiers, exhibits promise for broader application to a diverse range of deactivated air purification catalysts, potentially enabling implementation on a large scale.

Internal Electric Field Facilitates Facet-Dependent Photocatalytic Cl- Utilization on BiOCl in High-Salinity Wastewater for Ammonium Removal.

High Cl- concentration in saline wastewater (e.g., landfill leachate) limits wastewater purification. Catalytic Cl- conversion into reactive chlorine species (RCS) arises as a sustainable strategy, making the salinity profitable for efficient wastewater treatment. Herein, aiming to reveal the structure-property relationship in Cl- utilization, bismuth oxychloride (BiOCl) photocatalysts with coexposed {001} and {110} facets are synthesized. With an increasing {001} ratio, the RCS production efficiency increases from 75.64 to 96.89 µg L-1 min-1. Mechanism investigation demonstrates the fast release of lattice Cl- as an RCS and the compensation of ambient Cl-. Correlation analysis between the internal electric field (IEF, parallel to [001]) and normalized efficiency on {110} (kRCS/S{110}, perpendicular to [001]) displays a coefficient of 0.86, validating that the promoted carrier dynamics eventually affects Cl- conversion on the open layered structure. The BiOCl photocatalyst is well behaved in ammonium (NH4+-N) degradation ranging from 20 to 800 mg N L-1 with different chlorinity (3-12 g L-1 NaCl). The sustainable Cl- conversion into RCS also realizes 85.4% of NH4+-N removal in the treatment of realistic landfill leachate (662 mg of N L-1 NH4+-N). The structure-property relationship provides insights into the design of efficient catalysts for environment remediation using ambient Cl-.

Unravelling the Role of Free Radicals in Photocatalysis.

Free radicals are increasingly recognized as active intermediate reactive species that can participate in various redox processes, significantly influencing the mechanistic pathways of reactions. Numerous researchers have investigated the generation of one or more distinct photogenerated radicals, proposing various hypotheses to explain the reaction mechanisms. Notably, recent research has demonstrated the emergence of photogenerated radicals in innovative processes, including organic chemical reactions and the photocatalytic dissolution of precious metals. To harness the potential of these free radicals more effectively, it is imperative to consolidate and analyze the processes and action modes of these photogenerated radicals. This conceptual paper delves into the latest advancements in understanding the mechanics of photogenerated radicals.

Exceptional piezocatalytic H2 production of nitrogen-doped TiO2@carbon nanosheets induced by engineered piezoelectricity.

Piezocatalytic hydrogen evolution is a promising strategy to generate sustainable energy. In this report, nitrogen-doped (N-doped) TiO2@ carbon nanosheets (N-TiO2@C NSs) was successfully synthesized using C3N4 as a multifunctional template. During the synthesis, the two-dimensional (2D) architecture of C3N4 nanosheets directed the synthesis of TiO2 nanosheets. In addition, nitrogens of C3N4 were doped into the TiO2 lattice. Simultaneously, C3N4 was transformed into N-doped carbon nanosheets. N doping broke the crystal symmetry of TiO2, which endowed TiO2 with promising piezoelectric properties. The N-doped carbon nanosheets derived from C3N4 improved charge carrier separation efficiency and served as a flexible support to inhibit structural damage under sonication. Therefore, the N-TiO2@C NSs exhibited highly efficient activity for piezocatalytic H2 production (6.4 mmol·g-1·h-1) in the presence of methanol, much higher than those of the previously reported piezocatalysts. Our method is hoped to provide a new strategy for designing highly efficient piezocatalysts.

Aqueous Electroreduction of Nitric Oxide to Ammonia at Low Concentration via Vacancy Engineered FeOCl.

Electroreduction of nitric oxide (NO) to NH3 (NORR) has gained extensive attention for the sake of low carbon emission and air pollutant treatment. Unfortunately, NORR is greatly hindered by its sluggish kinetics, especially under low concentrations of NO. Herein, we developed a chlorine (Cl) vacancy strategy to overcome this limitation over FeOCl nanosheets (FeOCl-VCl ). Density functional theory (DFT) calculations revealed that the Cl vacancy resulted in defective Fe with sharp d-states characteristics in FeOCl-VCl to enhance the absorption and activation of NO. In situ X-ray absorption near-edge structure (XANES) and attenuated total reflection-infrared spectroscopy (ATR-IR) verified the lower average oxidation state of defective Fe to enhance the electron transfer for NO adsorption/activation and facilitate the generation of key NHO and NHx intermediates. As a result, the FeOCl-VCl exhibited superior NORR activities with the NH3 Faradaic efficiency up to 91.1 % while maintaining a high NH3 yield rate of 455.4 µg cm-2 h-1 under 1.0 vol % NO concentration, competitive with those of previously reported literatures under higher NO concentration. Further, the assembled Zn-NO battery utilizing FeOCl-VCl as cathode delivered a record peak power density of 6.2 mW cm-2 , offering a new route for simultaneous NO removal, NH3 production, and energy supply.

Fe2O3/TiO2/reduced graphene oxide-driven recycled visible-photocatalytic Fenton reactions to mineralize organic pollutants in a wide pH range.

Photocatalytic Fenton reactions combined the advantages from both photocatalysis and Fenton reaction in mineralizing organic pollutants. The key problems are the efficiency and recycling stability. Herein, we reported a novel Fe2O3/TiO2/reduced graphene oxide (FTG) nanocomposite synthesized by a facile solvothermal method. The TiO2 in FTG degraded organic pollutants and mineralized intermediates via photocatalysis under visible light irradiation, which could also promote Fenton reaction by accelerating Fe3+-Fe2+ recycle. Meanwhile, the Fe2O3 rapidly degraded organic pollutants via Fenton reactions, which also promoted photocatalysis by enhancing visible light absorbance and diminishing photoelectron-hole recombination. The high distribution of TiO2 and Fe2O3 on rGO, together with their strong interaction resulted in enhanced synergetic cooperation between photocatalysis and Fenton reactions, leading to the high mineralization efficiency of organic pollutants. More importantly, it could also inhibit the leaching of Fe species, leading to the long lifetime of FTG during photocatalytic Fenton reactions in a wide pH range from 3.4 to 9.2.

Photocatalytic Free Radical-Controlled Synthesis of High-Performance Single-Atom Catalysts.

Single-atom catalysts (SACs) have emerged as crucial players in catalysis research, prompting extensive investigation and application. The precise control of metal atom nucleation and growth has garnered significant attention. In this study, we present a straightforward approach for preparing SACs utilizing a photocatalytic radical control strategy. Notably, we demonstrate for the first time that radicals generated during the photochemical process effectively hinder the aggregation of individual atoms. By leveraging the cooperative anchoring of nitrogen atoms and crystal lattice oxygen on the support, we successfully stabilize the single atom. Our Pd1 /TiO2 catalysts exhibit remarkable catalytic activity and stability in the Suzuki-Miyaura cross-coupling reaction, which was 43 times higher than Pd/C. Furthermore, we successfully depose Pd atoms onto various substrates, including TiO2 , CeO2 , and WO3 . The photocatalytic radical control strategy can be extended to other single-atom catalysts, such as Ir, Pt, Rh, and Ru, underscoring its broad applicability.

2D MXenes polar catalysts for multi-renewable energy harvesting applications.

The synchronous harvesting and conversion of multiple renewable energy sources for chemical fuel production and environmental remediation in a single system is a holy grail in sustainable energy technologies. However, it is challenging to develop advanced energy harvesters that satisfy different working mechanisms. Here, we theoretically and experimentally disclose the use of MXene materials as versatile catalysts for multi-energy utilization. Ti3C2TX MXene shows remarkable catalytic performance for organic pollutant decomposition and H2 production. It outperforms most reported catalysts under the stimulation of light, thermal, and mechanical energy. Moreover, the synergistic effects of piezo-thermal and piezo-photothermal catalysis further improve the performance when using Ti3C2TX. A mechanistic study reveals that hydroxyl and superoxide radicals are produced on the Ti3C2TX under diverse energy stimulation. Furthermore, similar multi-functionality is realized in Ti2CTX, V2CTX, and Nb2CTX MXene materials. This work is anticipated to open a new avenue for multisource renewable energy harvesting using MXene materials.

Homogeneous Carbon Dot-Anchored Fe(III) Catalysts with Self-Regulated Proton Transfer for Recyclable Fenton Chemistry.

Fenton chemistry has been widely studied in a broad range from geochemistry, chemical oxidation to tumor chemodynamic therapy. It was well established that Fe3+/H2O2 resulted in a sluggish initial rate or even inactivity. Herein, we report the homogeneous carbon dot-anchored Fe(III) catalysts (CD-COOFeIII) wherein CD-COOFeIII active center activates H2O2 to produce hydroxyl radicals (•OH) reaching 105 times larger than that of the Fe3+/H2O2 system. The key is the •OH flux produced from the O-O bond reductive cleavage boosting by the high electron-transfer rate constants of CD defects and its self-regulated proton-transfer behavior probed by operando ATR-FTIR spectroscopy in D2O and kinetic isotope effects, respectively. Organic molecules interact with CD-COOFeIII via hydrogen bonds, promoting the electron-transfer rate constants during the redox reaction of CD defects. The antibiotics removal efficiency in the CD-COOFeIII/H2O2 system is at least 51 times large than the Fe3+/H2O2 system under equivalent conditions. Our findings provide a new pathway for traditional Fenton chemistry.

Noble-Metal-Metalloid Alloy Architectures: Mesoporous Amorphous Iridium-Tellurium Alloy for Electrochemical N2 Reduction.

Amorphous noble metals with high surface areas have attracted significant interest as heterogeneous catalysts due to the numerous dangling bonds and abundant unsaturated surface atoms created by the amorphous phase. However, synthesizing amorphous noble metals with high surface areas remains a significant challenge due to strong isotropic metallic bonds. This paper describes the first example of a mesoporous amorphous noble metal alloy [iridium-tellurium (IrTe)] obtained using a micelle-directed synthesis method. The resulting mesoporous amorphous IrTe electrocatalyst exhibits excellent performance in the electrochemical N2 reduction reaction. The ammonia yield rate is 34.6 µg mg-1 h-1 with a Faradaic efficiency of 11.2% at -0.15 V versus reversible hydrogen electrode in 0.1 M HCl solution, outperforming comparable crystalline and Ir metal counterparts. The interconnected porous scaffold and amorphous nature of the alloy create a complementary effect that simultaneously enhances N2 absorption and suppresses the hydrogen evolution reaction. According to theoretical simulations, incorporating Te in the IrTe alloy effectively strengthens the adsorption of N2 and lowers the Gibbs free energy for the rate-limiting step of the electrocatalytic N2 reduction reaction. Mesoporous chemistry enables a new route to achieve high-performance amorphous metalloid alloys with properties that facilitate the selective electrocatalytic reduction of N2.

Tailoring the Asymmetric Structure of NH2 -UiO-66 Metal-Organic Frameworks for Light-promoted Selective and Efficient Gold Extraction and Separation.

Designing adsorption materials with high adsorption capacities and selectivities is highly desirable for precious metal recovery. Desorption performance is also particularly crucial for subsequent precious metal recovery and adsorbent regeneration. Herein, a metal-organic framework (MOF) material (NH2 -UiO-66) with an asymmetric electronic structure of the central zirconium oxygen cluster has an exceptional gold extraction capacity of 2.04 g g-1 under light irradiation. The selectivity of NH2 -UiO-66 for gold ions is up to 98.8 % in the presence of interfering ions. Interestingly, the gold ions adsorbed on the surface of NH2 -UiO-66 spontaneously reduce in situ, undergo nucleation and growth and finally achieve the phase separation of high-purity gold particles from NH2 -UiO-66. The desorption and separation efficiency of gold particles from the adsorbent surface reaches 89 %. Theoretical calculations indicate that -NH2 functions as a dual donor of electrons and protons, and the asymmetric structure of NH2 -UiO-66 leads to energetically advantageous multinuclear gold capture and desorption. This adsorption material can greatly facilitate the recovery of gold from wastewater and can easily realize the recycling of the adsorbent.

A curtain purification system based on a rabbit fur-based rotating triboelectric nanogenerator for efficient photocatalytic degradation of volatile organic compounds.

Efficient removal of air pollution caused by volatile organic compounds (VOCs) and particulate matter (PM) through distributed energy collected from the environment is an effective strategy to achieve both energy conservation and better air quality. Herein, a curtain purification system based on a rabbit fur-based rotary triboelectric nanogenerator (RR-TENG) and a collaborative photocatalysis technology was designed for indoor air purification. The high electrostatic field from RR-TENG enhances formaldehyde adsorption, while it can also efficiently adsorb PM2.5 simultaneously. More interestingly, the ultrahigh electric field provided by RR-TENG promotes the separation of photogenerated electron-hole pairs of the g-C3N4/TiO2 composite photocatalyst, generating more superoxide radicals (⋅O2-), hydroxyl radicals (⋅OH), and holes (h+) and thereby improving the photocatalytic efficiency. In a simulated reaction chamber of 9 L, the formaldehyde removal rate of the system can reach 79.2% within 90 min and RR-TENG rapidly reduces PM2.5 from 999 µg m-3 to 50 µg m-3 within 60 s. This study proposes a curtain purification system integrating the function of energy collection and photocatalytic purification, which can be applied for improving air quality and human health.

Subsurface Engineering Induced Fermi Level De-pinning in Metal Oxide Semiconductors for Photoelectrochemical Water Splitting.

Photoelectrochemical (PEC) water splitting is a promising approach for renewable solar light conversion. However, surface Fermi level pinning (FLP), caused by surface trap states, severely restricts the PEC activities. Theoretical calculations indicate subsurface oxygen vacancy (sub-Ov ) could release the FLP and retain the active structure. A series of metal oxide semiconductors with sub-Ov were prepared through precisely regulated spin-coating and calcination. Etching X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and electron energy loss spectra (EELS) demonstrated Ov located at sub ∼2-5 nm region. Mott-Schottky and open circuit photovoltage results confirmed the surface trap states elimination and Fermi level de-pinning. Thus, superior PEC performances of 5.1, 3.4, and 2.1 mA cm-2 at 1.23 V vs. RHE were achieved on BiVO4 , Bi2 O3 , TiO2 with outstanding stability for 72 h, outperforming most reported works under the identical conditions.

Photocatalytic Dissolution of Precious Metals by TiO2 through Photogenerated Free Radicals.

Exploring the pathways for photocatalytic dissolution of precious metals (PMs) is crucial for optimizing recovery. In this work, we systematically investigated the selectivity and solvation effects observed for dissolution by focusing on photocatalysis, precious metals and solvents. By combining transient characterization, reaction kinetics, and density functional theory, we determined that the radicals generated in photocatalysis were the key active species in the entire reaction. The cyano functional group in the solvent was the driving factor for dissolution of gold, and the importance of chlorine radicals for dissolution of platinum group precious metals was further confirmed. In addition, the catalytic properties of different precious metals can promote different transformations of functional groups, leading to selective dissolution. The structures of photocatalytic precious metal leaches also precisely explains the special coordination forms of precious metals and functional group ligands.

Self-Cleaning and Shape-Adaptive Triboelectric Nanogenerator-Contained TiO2 Nanoparticle Coating.

With the rapid development of triboelectric nanogenerators (TENGs) for flexible wearable devices and electronic skins, challenges have gradually emerged related to the electrification surface, such as pollutant contamination and sophisticated surface adaptability. Hence, we report a simple spraying method to produce a shape-adaptive photocatalytic (SAP) triboelectric material with both self-cleaning and shape-adaptive functions. By spraying the polyvinyl alcohol solution with TiO2 photocatalysts and pre-drying cyclic, the SAP film can be adapted to a varied and intricate substrate. The highest transferred charge density of the SAP film reaches 197.5 µC/m2, when it contacts with the PTFE film. At the same time, it can degrade 74.4% of simulated pollutants under sunlight illumination, and 97% of the transferred charge density can be maintained after the degradation process, indicating good self-cleaning function and stable electrical output. Moreover, the spraying method of this allows it to have shape-adaptive functions. Accordingly, the SAP film can be deposited on the rectangular pyramid and hemispherical surface for fabricating TENGs with special shapes. This low-cost and simple spraying method further promotes the commercialized application of TENGs in the field of wearable devices and skin sensors.

Improving Degradation Efficiency of Organic Pollutants through a Self-Powered Alternating Current Electrocoagulation System.

Although electrocoagulation technology has been widely researched in wastewater treatment, high energy consumption and electrode passivation are still the main challenges for its widespread applications. Here, we propose a self-powered electrocoagulation system based on a triboelectric nanogenerator (TENG) with alternating current (AC) outputs to solve these two issues, and thus enhance the removal efficiency of organic pollutants. Compared with the direct current source, the AC power source can reduce the electrode passivation, produce more aluminum hydroxide compounds after consuming an equal amount of charges, and thus improve the degradation efficiency. Moreover, the removal efficiency can be further enhanced by decreasing the frequency AC, in which a 5.7-fold improvement was achieved at 0.2 Hz compared to DC at 1.8 Hz. Inspired by the low frequency of ocean wave water, we developed a self-powered AC-electrocoagulation system to directly drive the electrocoagulation reaction by harvesting water wave energy, which can effectively remove 94.8% of xylenol orange and 98.8% of water-oil emulsion, and thus completely address the problem of energy consumption. This study further promotes the application of self-powered electrochemical systems in treating environmental pollution.

Improved Degradation Efficiency of Levofloxacin by a Self-Powered Electrochemical System with Pulsed Direct-Current.

With the excellent structural design, rotary triboelectric nanogenerator (R-TENG) is suitable for harvesting mechanical energy such as wind energy and water energy to build a self-powered electrochemical system for environmental science. The electrochemical performance has been greatly improved by using the pulsed direct-current (PDC) output of a TENG; however, a full-wave PDC (FW-PDC) is hardly realized in R-TENG devices due to existence of phase superposition. Here, a R-TENG with FW-PDC output is reported to perform a self-powered electro-Fenton system for enhancing the removal efficiency of levofloxacin (OFL). By adjusting the rotation center angle ratio between each rotator and stator unit, the phase superposition of R-TENG caused by multiple parallel electrodes can be effectively eliminated, thus achieving the desired FW-PDC output. Because of the reduced electrode passivation effect, the removal efficiency of OFL is improved by 30% under equal electric charges through using the designed R-TENG with FW-PDC output compared to traditional R-TENG. This study provides a promising methodology to improve the performance of self-powered electrochemical process for treating environment pollutions.

Self-Driven Reactive Oxygen Species Generation via Interfacial Oxygen Vacancies on Carbon-Coated TiO2-x with Versatile Applications.

The effective activation and utilization of O2 have always been the focus of scientists because of its wide applications in catalysis, organic synthesis, life and medical science. Here, a novel method for activating O2 spontaneously via interfacial oxygen vacancies on carbon-coated TiO2-x to generate reactive oxygen species (ROS) with versatile applications is reported. The interfacial oxygen vacancies can be stabilized by the carbon layer and hold its intrinsic properties for spontaneous oxygen activation without light irradiation, while common surface oxygen vacancies on TiO2-x are always consumed by the capture of H2O to form the surface hydroxyls. Thus, O2 absorbed at the interface of carbon and TiO2-x can be directly activated into singlet oxygen (1O2) or superoxide radicals (·O2-), confirmed both experimentally and theoretically. These reactive oxygen species exhibit excellent performance in oxidation reactions and inhibition of MCF-7 cancer cells, providing new insight into the effective utilization of O2 via oxygen vacancies on metal oxides.

Polyaniline-TiO2 composite photocatalysts for light-driven hexavalent chromium ions reduction.

In order to develop efficient photocatalysts, great efforts have been made to reduce hexavalent chromium to trivalent chromium. The photocatalytic efficiency of this reduction depends largely on the adsorption and diffusion of hexavalent chromium ions on the surface of the photocatalyst. In this paper, polyaniline-TiO2 composite can effectively improve the photocatalytic reduction performance and stability of hexavalent chromium ion. The effect of polyaniline (PANI) thickness on Cr(VI) activity and stability of photocatalytic reduction was studied by adjusting the content of PANI on Mesoporous TiO2 (MT) surface. Under the irradiation conditions, the reaction results showed that the reduction rate was 100%, and the maximum reaction rate reached 0.62 min-1 when the PANI modification was 3.0%. Moreover, the results showed that the reduction performance remained 100% after ten cycles. The main reason is that the PANI modified on the surface of TiO2 is rich in positively charged amino group, which can efficiently adsorb the reactant Cr(VI), and make the product Cr(III) leave the reaction interface quickly, thus ensuring the performance of photocatalyst.

Correction to: Photoelectrochemical sensing of dopamine using gold-TiO2 nanocomposites and visible-light illumination.

The published version of this article, unfortunately, contains error. The author found out that Chinese characters are shown in Scheme 1a.