Electrostatic Self-Assembly of CdS Quantum Dots with Co9S8 Hollow Nanotubes for Enhanced Visible Light Photocatalytic H2 Production.

CdS quantum dots (CdS QDs) are regarded as a promising photocatalyst due to their remarkable response to visible light and suitable placement of conduction bands and valence bands. However, the problem of photocorrosion severely restricts their application. Herein, the CdS QDs-Co9S8 hollow nanotube composite photocatalyst has been successfully prepared by loading Co9S8 nanotubes onto CdS QDs through an electrostatic self-assembly method. The experimental results show that the introduction of Co9S8 cocatalyst can form a stable structure with CdS QDs, and can effectively avoid the photocorrosion of CdS QDs. Compared with blank CdS QDs, the CdS QDs-Co9S8 composite exhibits obviously better photocatalytic hydrogen evolution performance. In particular, CdS QDs loaded with 30% Co9S8 (CdS QDs-30%Co9S8) demonstrate the best photocatalytic performance, and the H2 production rate reaches 9642.7 µmol·g-1·h-1, which is 60.3 times that of the blank CdS QDs. A series of characterizations confirm that the growth of CdS QDs on Co9S8 nanotubes effectively facilitates the separation and migration of photogenerated carriers, thereby improving the photocatalytic hydrogen production properties of the composite. We expect that this work will facilitate the rational design of CdS-based photocatalysts, thereby enabling the development of more low-cost, high-efficiency and high-stability composites for photocatalysis.

One-step rapid colorimetric detection of K+ using silver nanoparticles modified by crown ether.

Urinary potassium is an important parameter in clinical health diagnosis. Rapid and convenient detection of potassium ions (K+) in urine is essential for personal healthcare and health management. Here, crown ether (4-aminodibenzo-18-crown-6, ADC) modified silver nanoparticles (ADC-Ag NPs) were successfully prepared for one-step rapid colorimetric detection of urinary potassium. The detection mechanism is as follows: due to the matching sizes of the diameter of K+ and the cavity in crown ether 6, K+ is encapsulated between the cavities of two crown ethers, resulting in the clumping of ADC-Ag NPs and the color of the solution being altered. The colorimetric detection method has a fast response and is completed within 20 minutes. It also shows good selectivity and interference immunity. The lowest detectable concentration is 20 µM with the naked eye and 2.16 µM for UV-vis absorption spectroscopy. A good linear relationship (R2 = 0.9931) between the absorption intensity ratio and K+ concentration (0-100 µM) indicates that this colorimetric probe can be used to detect K+. The method was also applied for quantitative analysis of K+ in real urine samples with recovery between 116 and 120%.

One-Pot Synthesis of N-Doped NiO for Enhanced Photocatalytic CO2 Reduction with Efficient Charge Transfer.

The green and clean sunlight-driven catalytic conversion of CO2 into high-value-added chemicals can simultaneously solve the greenhouse effect and energy problems. The controllable preparation of semiconductor catalyst materials and the study of refined structures are of great significance for the in-depth understanding of solar-energy-conversion technology. In this study, we prepared nitrogen-doped NiO semiconductors using a one-pot molten-salt method. The research shows that the molten-salt system made NiO change from p-type to n-type. In addition, nitrogen doping enhanced the adsorption of CO2 on NiO and increased the separation of photogenerated carriers on the NiO. It synergistically optimized the CO2-reduction system and achieved highly active and selective CO2 photoreduction. The CO yield on the optimal nitrogen-doped photocatalyst was 235 µmol·g-1·h-1 (selectivity 98%), which was 16.8 times that of the p-type NiO and 2.4 times that of the n-type NiO. This can be attributed to the fact that the nitrogen doping enhanced the oxygen vacancies of the NiOs and their ability to adsorb and activate CO2 molecules. Photoelectrochemical characterization also confirmed that the nitrogen-doped NiO had excellent electron -transfer and separation properties. This study provides a reference for improving NiO-based semiconductors for photocatalytic CO2 reduction.

Cd0.5Zn0.5S/CoWO4 Nanohybrids with a Twinning Homojunction and an Interfacial S-Scheme Heterojunction for Efficient Visible-Light-Induced Photocatalytic CO2 Reduction.

The construction of a phase junction photocatalyst can significantly enhance the photocatalytic performance with high selectivity for CO2 reduction. In this study, an S-scheme junction Cd0.5Zn0.5S/CoWO4 semiconductor with the coupling of a twin crystal Cd0.5Zn0.5S homojunction and CoWO4 was designed through a hydrothermal method, which could convert CO2 to CO with high efficiency under visible-light illumination. Cd0.5Zn0.5S-10%CoWO4 exhibited the optimal performance and its CO yield and selectivity were up to 318.68 µmol·g-1 and 95.90%, respectively, which were 4.54 and 1.62 times higher than that of twin crystal Cd0.5Zn0.5S. Moreover, the Cd0.5Zn0.5S homojunction with a zinc-blende and wurtzite phase and the S-scheme phase junction of Cd0.5Zn0.5S/CoWO4 enhanced the property of CO2 adsorption and accelerated the detachment of photogenerated carriers. The combination of photogenerated holes in Cd0.5Zn0.5S and the electrons of CoWO4 can retain the reduction sites to improve photocatalytic performance. This study provides a neoteric concept and reference for the construction of the S-scheme phase junction.

Adsorptive removal of phosphate from water using mesoporous materials: A review.

Mesoporous materials have significant potential for use as adsorbents for removal of phosphate from water. The chemical and structural properties of materials greatly affect their capacity and rate in the phosphate adsorption process. This paper reviews recent activities in the development of mesoporous materials as phosphate adsorbents. In particular, it mainly focuses on the synthesis, properties and phosphate removal efficiency of various materials with mesoporosity, including metal-coordinated amino-functionalized silicas, ammonium-functionalized silicas, metal-doped mesoporous silicas, metal oxides, metal sulfate and carbon.

La/Ce-codoped Bi2O3 composite photocatalysts with high photocatalytic performance in removal of high concentration dye.

A series of La/Ce-codoped Bi2O3 composite photocatalysts were fabricated via hydrothermal-calcination process. The as-prepared products were intensively characterized by some physicochemical characterizations like N2 physical adsorption, X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), UV-Vis diffuse reflectance (UV-Vis DRS), Fourier transform infrared spectroscopy (FT-IR), photoelectrochemical measurements, and photoluminescence (PL) spectroscopy. The characterization results indicated that La and Ce doping induced obvious crystal phase transformation in Bi2O3, from monoclinic to tetragonal phase. La and Ce codoping also gave rise to the obvious synergetic effects, e.g., the lattice contraction of Bi2O3, the decrease of crystal size and the increase of surface area. The photocatalytic performance of the prepared catalysts was evaluated by removal of dye acid orange II with high concentration under visible light irradiation. Results showed that La/Ce-codoped Bi2O3 displayed much higher photocatalytic performance than that of bare Bi2O3, single La or Ce doped Bi2O3 samples. The superior photocatalytic activity was mainly attributed to the improved texture and surface properties and the synergistic effects of La and Ce codoping on suppressing the recombination of photo-generated electrons (e-) and holes (h+).

Perylene diimide/iron phthalocyanine Z-scheme heterojunction with strong interfacial charge transfer through π-π interaction: Efficient photocatalytic degradation of tetracycline hydrochloride.

The development of an all-organic Z-scheme heterojunction photocatalyst with the matched band structure, efficient electron transfer and excellent photocatalytic performance is valuable for a sustainable future. A novel perylene diimide/phthalocyanine iron (PDI/FePc) heterojunctions with strong π-π interaction were synthesized by a self-assembled method, which exhibited strong visible-light-driven photocatalytic degradation activities of tetracycline hydrochloride (TC). The TC removal rate over PDI/FePc was achieved three times and 87.5 times higher than that of PDI and FePc. PDI/FePc (131.1 mv·dec-1) presented a lower Taffel slope than that of PDI (228.6 mv·dec-1) for the oxidation. This may be due to the strong π-π interactions between PDI and FePc, which can reduce the layer spacing of the supramolecular structure and facilitate the separation and transfer of photogenerated carriers in the built-in electric field. In addition, radical quenching tests revealed that superoxide radicals (•O2-) acted as a dominant role in photocatalytic oxidation. An increscent specific surface area of PDI decorated by FePc also gave the rapid pathway for charge transfer and enhanced the adsorption ability. This provides a new idea for the formation of heterojunction to improve the photocatalytic activity of organic supramolecular materials.

Integrating Co(OH)2 nanosheet arrays on graphene for efficient noble-metal-free EY-sensitized photocatalytic H2 evolution.

The development of an efficient noble-metal-free cocatalyst is the key to photocatalytic hydrogen production technology. In this study, hierarchical Co(OH)2 nanosheet array-graphene (GR) composite cocatalysts are developed. With Eosin Y (EY) as a photosensitizer, the optimal Co(OH)2-10%GR hybrid cocatalyst presents excellent photocatalytic activity with an H2 production rate of 17 539 µmol g-1 h-1, and the apparent quantum yield for hydrogen production can reach 12.8% at 520 nm, which remarkably surpasses that of pure Co(OH)2 and most similar hybrid cocatalyst systems. Experimental investigations demonstrate that the excellent photocatalytic activity of Co(OH)2-GR arises from its unique nanosheet array architecture, which can collaboratively expose rich active sites for photocatalytic hydrogen evolution and facilitate the migration and separation of photogenerated charge carriers. It is desired that this study would supply a meaningful direction for the rational optimization of the constitute and structure of cocatalysts to achieve efficient photocatalytic hydrogen generation.

Photocatalytic H2O2 production and removal of Cr (VI) via a novel Lu3NbO7: Yb, Ho/CQDs/AgInS2/In2S3 heterostructure with broad spectral response.

The low-usage of solar energy and the sluggish separation efficiency of the photogenerated electrons/holes pairs are the obstacles in the practical application of photocatalysts. The integration of upconversion and Z-scheme heterojunction is expected to break the barriers to achieve the efficient charge separation and broaden near-infrared light absorption. Herein, an effective indirect Z scheme AgInS2/In2S3 heterostructure with carbon quantum dots (CQDs, as the electron conduction medium) and Lu3NbO7:Yb, Ho (as upconversion function) has been successfully synthesized. Consequently, the Lu3NbO7: Yb, Ho/CQDs/AgInS2/In2S3 heterostructure exhibited superior photocatalytic activities for Cr(VI) reduction and H2O2 production, reducing 99.9% of Cr(VI)(20 ppm, 15 min) and 78.5% of Cr(VI) (40 ppm, 30 min) with visible light irradiation as well as 94.0% of Cr(VI) (20 ppm, 39 min) under NIR light irradiation. Simultaneously, the heterostructure could generate 902.9 µM H2O2 for 5 h under visible light irradiation. The intensive photocatalytic properties could primarily be attributed to the boosted light absorption capacity, the improved solar-to-energy conversion by the remarkable upconversion capacity of Lu3NbO7: Yb, Ho/CQDs and the faster charge transfer through a Z-schematic pathway. This work is anticipated to open a novel "window" for designing the efficient photocatalysts by coupling of Lu3NbO7: Yb, Ho and CQDs.

Visible and near-infrared driven Yb3+/Tm3+ co-doped InVO4 nanosheets for highly efficient photocatalytic applications.

To effectively enhance the utilization of clean sunlight energy, harvesting a large percentage of near infrared (NIR) light is significant. One of the commonly used effective methods for modifying semiconductors is by co-doping upconversion materials on semiconductors to heighten the photocatalytic efficiency. In this work, Yb3+/Tm3+ co-doped InVO4 nanosheets were synthesized by a facile hydrothermal path, and the crystal phases, morphologies, surface chemical compositions, as well as optical properties were characterized. Yb3+/Tm3+ co-doped InVO4 revealed significantly enhanced photoactivity towards chromium(vi) reduction and methyl orange oxidation under visible or NIR light irradiation. Furthermore, 5YT-IV presented the highest electrocatalytic performance and photocatalytic production of H2O2 under visible light irradiation, requiring low overpotential and low Tafel slope (390 mV dec-1) for hydrogen evolution reaction than that of the bare InVO4 (731 mV dec-1), and as well improved the yield of photocatalytic H2O2 production by about 3.5 times. This was primarily ascribed to intensive light absorption resulting from the benign upconversion energy transfer of Yb3+/Tm3+ and the boosted charge separation caused by the intermediate energy states. Moreover, the presence of h+ and ˙O2- as the main oxidative species played a significant role during the photocatalytic oxidation process of methyl orange and electrons played a decisive role in Cr(vi) reduction. This study provides a promising platform for efficiently utilizing the visible-NIR energy of sunlight in the field of photocatalytic H2O2 production and for alleviating environmental pollution in future.

A microalgae residue based carbon solid acid catalyst for biodiesel production.

Biodiesel production from microalgae is recognized as one of the best solutions to deal with the energy crisis issues. However, after the oil extraction from the microalgae, the microalgae residue was generally discarded or burned. Here a novel carbon-based solid acid catalyst derived from microalgae residue by in situ hydrothermal partially carbonization were synthesized. The obtained catalyst was characterized and subjected to both the esterification of oleic acid and transesterification of triglyceride to produce biodiesel. The catalyst showed high catalytic activity and can be regenerated while its activity can be well maintained after five cycles.

Evaluation of flocculation induced by pH increase for harvesting microalgae and reuse of flocculated medium.

Flocculation induced by pH increase for harvesting microalgae and reuse of flocculated medium were evaluated. Increasing the medium pH value induced the highest flocculation efficiency of up to 90% for freshwater microalgae (Chlorella vulgaris, Scenedesmus sp., Chlorococcum sp.) with low/medium biomass concentrations and marine microalgae (Nannochloropsis oculata, Phaeodactylum tricornutum). The mechanism may be explained that Mg(2+) in the growth medium hydrolyzed to form magnesium hydroxide precipitate, which coagulated microalgal cells by sweeping flocculation and charge neutralization. Additionally, this study revealed that the microalgal biomass concentrations and released polysaccharide (RPS) from microalgae could influence the flocculation efficiencies. Furthermore, neutralizing pH and then supplementing nutrients allowed the flocculated medium to maintain an approximate growth yield to that of the fresh medium in algal cultivation. These results suggest that the method presented here is effective, and allows the reuse of the flocculated medium, thereby contributing to the economic production from algae to biodiesel.