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Rechargeable batteries are promising platforms for sustainable development of energy conversion and storage technologies. Highly efficient multifunctional electrodes based on bimetallic sulfides for rechargeable batteries are extremely desirable but still challenging to tailor with controllable phase and structure. Here, we report a colloidal strategy to fabricate FeCo-based bimetallic sulfides on reduced graphene oxide (rGO), which are expected to display highly efficient oxygen electrocatalysis and sodium storage performances. Specifically, as-screened FeCo8S8 nanosheets (NSs) on rGO originating from suitable tailoring of the Co9S8 matrix with Fe at the atomic level exhibited a very low potential difference (0.77 V) at 10 mA cm-2 and negligible voltage loss after 200 cycles as an air electrode for Zn-air batteries. For Na-ion batteries, FeCo8S8 NS/rGO demonstrated a superior high-rate capability (188 mAh g-1 at 20 A g-1) with long-term cycling stability. The bifunctional electrocatalytic property and sodium storage performance are attributed to not only the synergistic effect of Fe/Co but also the optimized catalytic activity and ion transport ability by the in situ rGO hybrid. This work demonstrates the potential applications of FeCo-based bimetallic sulfides as efficient electrode materials for both rechargeable Zn-air and Na-ion batteries.

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.

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.

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.

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 H(2)O(2) 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 (1)O(2) 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.

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 munic...

Bismuth oxychloride (BiOCl) is a typical UV-light-sensitive photocatalyst with a unique layered structure, but exhibits no response towards visible light. This is a main limitation for its practical applications in photocatalytic degradation of pollutants. Among various methods to expand the light absorption region, doping modification is an efficient approach because it can tailor the band structure by forming a doping energy level without changing the layered structure substantially. In this case, the static electric field in the BiOCl crystal can be retained. Since cobalt (Co) exhibits good electrochemical properties, it is an ideal element for doping modification to expand the light absorption region and enhance the charge separation efficiency of BiOCl. In this work, Co-doped BiOCl nanosheets were prepared using a simple hydrothermal route. The doped Co expanded the light absorption region and enhanced the charge separation efficiency by forming a doping energy level in the band gap of BiOCl. As a result, the Co-BiOCl nanosheets exhibited an outstanding photocatalytic performance in degrading bisphenol A (BPA) under visible light irradiation with a degradation rate of 3.5 times higher than that of BiOCl. On the basis of the experimental results and density functional theory calculations, the mechanism of visible-light-driven catalytic BPA degradation by the Co-BiOCl nanosheets was elucidated. Therefore, the feasibility of Co-doping modification for BiOCl was confirmed, and a novel and efficient strategy was provided for the design and synthesis of high-performance photocatalysts.

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.

Photocatalyst plays a vital role in the photochemical water treatment. To improve the visible-light photoactivity of TiO2 for refractory pollutant degradation, CdS/TiO2 hybrids with different nanostructures have been prepared, but usually suffer from a low photocatalytic degradation efficiency and a rapid photocorrosion. In this work, we developed a synergistic ZnO/CdS/TiO2 hybrid, which could act as a robust and self-protected photocatalyst for water purification without additional sacrificial reagents. This was attributed to the two different junction mechanisms in one single hybrid. Photons were selectively adsorbed by ZnO and CdS, then, the electrons with a low reductive activity in ZnO recombined directly with the holes with a low oxidative activity in CdS, whereas the holes with a high oxidative activity in ZnO and the electrons with a high reductive activity in CdS were captured for catalytic reaction. The superiority of the novel ZnO/CdS/TiO2 hybrid over the traditional CdS/TiO2 hybrid in both photocatalytic activity and anti-photocorrosion capacity was demonstrated in the degradation of Atrazine and Rhodamine B, two typical refractory organic pollutants, and the treatment of real textile wastewater under solar light irradiation. The developed ZnO/CdS/TiO2 hybrid exhibited an excellent potential for the degradation of refractory pollutants, and provided a new way to advance intrinsically solar-susceptible catalyst for photochemical wastewater treatment.

Fenton reaction is widely used for hazardous pollutant degradation. Reducing agents (RAs) have been proven to be efficient in promoting the generation of HO• in Fenton reaction by accelerating the redox cycle of Fe3+/Fe2+. However, the roles of different RAs in Fenton reaction remain unrevealed. In this work, the catalytic activity of three RAs, i.e., hydroxylamine (NH2OH), ascorbic acid (AA) and cysteine (Cys), on the degradation of benzoic acid (BA) and the hydroxyl radical formation in the Fenton-RAs system were investigated. Results show the catalytic performance of RAs in BA degradation by Fenton reaction followed an order of NH2OH > AA > Cys. Compared with the conventional Fenton system, the effective pH range in the Fenton-NH2OH system extended from 3.0 to 5.0, while the optimal pH in the Fenton-AA and Fenton-Cys systems ranged from 3.0 to 4.0. The Fenton-AA system exhibited a two-stage reaction toward BA degradation, which was different from the Fenton-NH2OH and Fenton-Cys systems. Furthermore, the dosing manner of AA was found to be a key factor governing its role in the Fenton-AA system. This observation suggests the different mechanisms behind the enhancement of the three RAs in Fenton system. Different from NH2OH and Cys, AA would inhibit the generation of HO•, especially at the fast stage of degradation process, where Fe3+ has not accumulated yet. In addition, the economic analysis using the electrical energy per order indicates Fenton-NH2OH system was economically feasible with the lowest energy input, compared to Fenton-AA and Fenton-Cys systems. These results are useful to better understand the roles of RAs in Fenton system, and also provide guidance about the selection and dosing manner of suitable RAs in the advanced oxidation processes.

TiO2 is capable of directly utilizing solar energy for sustainable energy harvest and water purification. Facet-dependent performance of TiO2 has attracted enormous interests due to its tunable photocatalytic activity toward photoredox transformations, but information about the noble-metal-loaded TiO2 for its facet-dependent photocatalytic performance, especially in pollutant degradation systems, is limited. In this work, inspired by our previous theoretical calculations about the roles of the crystal surface in Pt-loaded TiO2 in its enhanced photocatalytic capacity, TiO2 nanocrystals with interspersed polyhedron nanostructures and coexposed (001) and (101) surfaces as a support of Pt nanoparticles are prepared in a simple and relatively green route. Also, their performance for photocatalytic degradation of nitrobenzene (NB), a model organic pollutant, is explored. The experimental results demonstrate that the NB photodegradation and photoconversion efficiencies are significantly enhanced by uniformly loading Pt nanoparticles on the crystal surfaces, but the Pt nanoparticles deposited on only the (101) surface have no contribution to the improved NB photodegradation. Furthermore, the liquid chromatography mass spectrometry results also show that NB photodegradation tends to proceed on the (001) surface of Pt/TiO2 for the generation of nitrophenol intermediates through the photooxidation pathway. This work provides a new route to design and construct advanced photocatalysts toward pollutant photoredox conversions and deepens our fundamental understanding about crystal surface engineering.

This work aims to quantify sulfate ion concentrations in the system Na2SO4-H2O using Raman micro-spectroscopy. Raman spectra of sodium sulfate solutions with known concentrations were collected at ambient temperature (293 K) and in the 500 cm−1–4000 cm−1 spectral region. The results indicate that the intensity of the SO42– band increases with increasing concentrations of sulfate ion. A linear correlation was found between the concentration of SO42– (c) and parameter I1, which represents the ratio of the area of the SO42– band to that of the O-H stretching band of water (As/AW): I1 = –0.00102+0.01538c. Furthermore, we deconvoluted the O-H stretching band of water (2800 cm−1–3800 cm−1) at 3232 and 3430 cm−1 into two sub-Gaussian bands, and then defined Raman intensity of the two sub-bands as AB1 (3232 cm−1) and AB2 (3430 cm−1), defined the full width of half maximum (FWHM) of the two sub-bands as WB1 (3232 cm−1) and WB2 (3430 cm−1). A linear correlation between the concentration of SO42– (c) and parameter I2, which represents the ratio of Raman intensity of SO42– (As) (in 981 cm−1) to (AB1+AB2), was also established: I2=–0.0111+0.3653c. However, no correlations were found between concentration of SO42–(c) and FWHM ratios, which includes the ratio of FWHM of SO42– (Ws) to WB1, WB2 and WB1+B2 (the sum of WB1 and WB2), suggesting that FWHM is not suitable for quantitative studies of sulfate solutions with Raman spectroscopy. A comparison of Raman spectroscopic studies of mixed Na2SO4 and NaCl solutions with a constant SO42– concentration and variable Cl− concentrations suggest that the I1 parameter is affected by Cl−, whereas the I2 parameter was not Therefore, even if the solution is not purely Na2SO4-H2O, SO42– concentrations can still be calculated from the Raman spectra if the H2O band is deconvoluted into two sub-bands, making this method potentially applicable to analysis of natural fluid inclusions.

The cathodic material plays an essential role in oxygen reduction reaction for energy conversion and storage systems. Titanium dioxide, as a semiconductor material, is usually not recognized as an efficient oxygen reduction electrocatalyst owning to its low conductivity and poor reactivity. Here we demonstrate that nano-structured titanium dioxide, self-doped by oxygen vacancies and selectively exposed with the high-energy {001} facets, exhibits a surprisingly competitive oxygen reduction activity, excellent durability and superior tolerance to methanol. Combining the electrochemical tests with density-functional calculations, we elucidate the defect-centred oxygen reduction reaction mechanism for the superiority of the reductive {001}-TiO2−x nanocrystals. Our findings may provide an opportunity to develop a simple, efficient, cost-effective and promising catalyst for oxygen reduction reaction in energy conversion and storage technologies., Titanium dioxide is not generally considered to be an effective oxygen reduction catalyst. Here, the authors show that nanostructured titanium dioxide, self-doped with oxygen vacancies and with exposed high-energy {001} facets, exhibits competitive oxygen reduction catalytic activity and durability.

Titania modified with nanosized metallic clusters is found to substantially enhance its photocatalytic capacity for renewable energy generation and environmental purification, but the underlying mechanism, especially the roles of crystal surface in noble-metal-loaded TiO2, remain unclear. In this work, such roles in the Pt-loaded anatase TiO2 for the photocatalytic conversion of nitrobenzene (NB), a model pollutant, are explored by first-principle calculations. The theoretical calculations reveal that the Pt-TiO2 complex has a higher catalytic activity toward NB conversion than pure Pt clusters, and the (001) facets of TiO2 in this complex tend to accumulate more positively charged holes and thus have a higher photocatalytic activity than the (101) facets. Furthermore, the thermodynamic and kinetic results also show that the Pt cluster loaded on the (001) surface of anatase TiO2 is favored for NB conversion in the photooxidation pathway. This work deepens our fundamental understanding on the evolution of molecule-photocatalyst interface and provides implications for designing and preparing photocatalysts.

A novel model of two-dimensional periodically poled lithium niobate designed for second harmonic generation of 1064 nm is proposed, in which a rectangular light route is used. The effective length of the sample is longer than the sample real length by (5/3).21/2 times. The conversion efficiency enhances greatly without prolonging the periodically poled crystal length.

A two-dimensional periodically poled lithium niobate crystal with a 13.64 μm period was fabricated. The inverted duty cycle was about 23%. The second harmonic output for the second-order quasi-phase-matching (QPM) against the input was measured. The maximum second harmonic internal conversion efficiency was higher than 40%. All results implied that the second-order QPM could be used to obtain high-frequency conversion efficiency. Compared with the first-order QPM, the second-order QPM can reduce the requirement for the poling technique and the mask fabrication.

The periodic disturbance in transmittance of the polystyrene photonic crystal with a diameter of 3μm is observed in our experiment. According to the peak-to-peak intervals of the periodic disturbance, it can be seen that the periodic disturbance does not come from Mie scattering or Bragg diffraction, but from the propagation of whispering gallery mode in polystyrene spheres. The results show new potential applications of phtonic crystals.