Step-scheme porous g-C3N4/Zn0.2Cd0.8S-DETA composites for efficient and stable photocatalytic H2 production

In recent years,environmental pollution and energy crisis have become increasingly serious issues owing to the burning of fossil fuels.Among the many technologies,decomposition of water to produce hydrogen has attracted much attention because of its sustainability and non-polluting characteristic.However,highly efficient decomposition of water that is driven by visible light is still a challenge.Herein,we report the large-scale preparation of step-scheme porous graphite carbon nitride/Zn0.2Cd0.8S-diethylenetriamine(Pg-C3N4/Zn0.2Cd0.8S-DETA)composite by a facile solvothermal method.It was found by UV-vis spectroscopy that 15%Pg-C3N4/Zn0.2Cd0.8S-DETA exhibited suitable visible absorption edge and band gap for water decomposition.The hydrogen production rate of 15%Pg-C3N4/Zn0.2Cd0.8S-DETA composite was 6.69 mmol g^-1 h^-1,which was 16.73,1.61,and 1.44 times greater than those of Pg-C3N4,CdS-DETA,and Zn0.2Cd0.8S-DETA,respectively.In addition,15%Pg-C3N4/Zn0.2Cd0.8S-DETA composite displayed excellent photocatalytic stability,which was maintained for seven cycles of photocatalytic water splitting test.We believe that 15%Pg-C3N4/Zn0.2Cd0.8S-DETA composite can be a valuable guide for the development of solar hydrogen production applications in the near future.

A novel step-scheme BiVO4/Ag3VO4 photocatalyst for enhanced photocatalytic degradation activity under visible light irradiation

Over the past few years,the emission of organic pollutants into the environment has increased tremendously.Therefore,various photocatalysts have been developed for the degradation of organic pollutants.In this study,a step-scheme BiVO4/Ag3VO4 composite was synthesized via a hydrothermal and chemical deposition process for the degradation of methylene blue.The composite showed strong redox ability under visible light.The 40%BiVO4/Ag3VO4 composite showed excellent photocatalytic degradation properties with a Kapp of 0.05588 min^–1,which is 22.76 and 1.76 times higher than those of BiVO4(0.00247 min^–1)and Ag3VO4(0.03167 min^–1),respectively.The composite showed a stable performance and could retain 90%of its photocatalytic activity even after four cycles.The improved catalytic performance of the composite as compared to BiVO4 and Ag3VO4 can be attributed to its novel step-scheme mechanism,which facilitated the separation of the photogenerated charges and increased their lifetime.The photoluminescence measurement results and transient photocurrent response revealed that the composite showed efficient extraction of charge carriers.

Preparation of Z-scheme WO_3(H_2O)_(0.333)/Ag_3PO_4 composites with enhanced photocatalytic activity and durability

Ag3PO4 is widely used in the field of photocatalysis because of its unique activity. However, photocorrosion limits its practical application. Therefore, it is very urgent to find a solution to improve the light corrosion resistance of Ag3PO4. Herein, the Z-scheme WO3(H2O)0.333/Ag3PO4 composites are successfully prepared through microwave hydrothermal and simple stirring. The WO3(H2O)0.333/Ag3PO4 composites are characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and UV-Vis spectroscopy. In the degradation of organic pollutants, WO3(H2O)0.333/Ag3PO4 composites exhibit excellent performance under visible light. This is mainly attributed to the synergy of WO3(H2O)0.333 and Ag3PO4. Especially, the photocatalytic activity of 15%WO3(H2O)0.333/Ag3PO4 is the highest, and the methylene blue can be completely degraded in 4 min. In addition, the stability of the composites is also greatly enhanced. After five cycles of testing, the photocatalytic activity of 15%WO3(H2O)0.333/Ag3PO4 is not obviously decreased. However, the degradation efficiency of Ag3PO4 was only 20.2%. This indicates that adding WO3(H2O)0.333 can significantly improve the photoetching resistance of Ag3PO4. Finally, Z-scheme photocatalytic mechanism is investigated.

Construction of Z-scheme Ag_3PO_4/Bi_2WO_6 composite with excellent visible-light photodegradation activity for removal of organic contaminants

Ag3PO4has good potential for use in photocatalytic degradation of organic contaminants.However,the activity and stability of Ag3PO4is hard to sustain because of photocorrosion and the positive potential of the conduction band of Ag3PO4.In this study,A composite consisting of Bi2WO6nanosheets and Ag3PO4was developed to curb recombination of charge carriers and enhance the activity and stability of the catalyst.Formation of a Ag3PO4/Bi2WO6composite was confirmed using X‐ray diffraction,energy‐dispersive X‐ray spectroscopy,and X‐ray photoelectron spectroscopy.Photoluminescence spectroscopy provided convincing evidence that compositing Bi2WO6with Ag3PO4effectively reduced photocorrosion of Ag3PO4.The Ag3PO4/Bi2WO6composite gave a high photocatalytic performance in photodegradation of methylene blue.A degradation rate of0.61min?1was achieved;this is1.3and6.0times higher than those achieved using Ag3PO4(0.47min?1)and Bi2WO6(0.10min?1),respectively.Reactive species trapping experiments using the Ag3PO4/Bi2WO6composite showed that holes,?OH,and?O2?all played specific roles in the photodegradation process.The photocatalytic mechanism was investigated and a Z‐scheme was proposed as a plausible mechanism.

Novel closed-cycle reaction mode for totally green production of Cu_(1.8)Se nanoparticles based on laser-generated Se colloidal solution

Non-stoichiometric copper selenide(Cu_(2-x)Se,x=0.18~0.25)nanomaterials have attracted extensive attentions due to their excellent thermoelectric,optoelectronic and photocatalytic performances.However,efficient production of Cu_(2-x)Se nanoparticles(NPs)through a green and convenient way is still hindered by the inevitable non-environmentally friendly operations in common chemical synthesis.Herein,we initially reveal the coexistence of seleninic acid content and elemental selenium(Se)NPs in pulsed laser-generated Se colloidal solution.Consequently,we put forward firstly a closedcycle reaction mode for totally green production of Cu_(1.8)Se NPs to exclude traditional requirements of high temperature and toxic precursors by using Se colloidal solution.In such closed-cycle reaction,seleninic acid works as the initiator to oxidize copper sheet to release cuprous ions which can catalyze the disproportion of Se NPs to form Se O_(3)^(2-)and Se^(2-)ions and further produce Cu_(2-x)Se NPs,and the by-product SeO_(3)^(2-)ions promote subsequent formation of cuprous from the excessive Cu sheet.In experiments,the adequate copper(Cu)sheet was simply dipped into such Se colloidal solution at 70℃,and then the stream of Cu_(1.8)SeNPs could be produced until the exhaustion of selenium source.The conversion rate of Se element reaches to more than 75%when the size of Se NPs in weakly acidic colloidal solution is limited between 1 nm and 50 nm.The laser irradiation duration shows negative correlation with the size of Se NPs and unobvious impact to the p H of the solution which both are essential to the high yield of Cu_(1.8)SeNPs.Before Cu sheet is exhausted,Se colloidal solution can be successively added without influences to the product quality and the Se conversion rate.Such green methodology positively showcases a brand-new and potential strategy for mass production of Cu_(2-x)Se nanomaterials.

Perspective on how laser-ablated particles grow in liquids

Laser ablation in liquids has emerged as a new branch of nanoscience for developing various nanomaterials with different shapes.However, how to design and control nanomaterial growth is still a challenge due to the unique chemical-physical process chain correlated with nanomaterial nucleation and growth, including plasma phase(generation and rapid quenching), gas(bubble) phase,and liquid phase. In this review, through summarizing the literature about this topic and comparing with the well-established particle growth mechanisms of the conventional wet chemistry technique, our perspective on the possible nanoparticle growth mechanisms or routes is presented, aiming at shedding light on how laser-ablated particles grow in liquids. From the microscopic viewpoint, the nanoparticle growth contains six mechanisms, including LaMer-like growth, coalescence, Ostwald ripening, particle(oriented) attachment, adsorbate-induced growth and reaction-induced growth. For each microscopic growth mechanism, the vivid growth scenes of some representative nanomaterials recorded by TEM and SEM measurements are displayed. Afterwards,the scenes from the macroscopic viewpoint for the large submicro-and micro-scale nanospheres and anisotropic nanostructures formation and evolution from one nanostructure into another one are presented. The panorama of how diverse nanomaterials grow during and after laser ablation in liquids shown in this review is intended to offer a overview for researchers to search for the possible mechanisms correlated to their synthesized nanomaterials, and more expectation is desired to better design and tailor the morphology of the nanocrystals synthesized by LAL technique.

Diverse nanomaterials synthesized by laser ablation of pure metals in liquids

Diverse nanomaterials, in the forms of carbides, sulfides, oxides, metals, hydroxides, etc., have been synthesized by laser ablation in liquids(LAL) with metal targets as the dominant educts. Many advantages of LAL technique itself and its products have been revealed since 1983 when the first report about LAL was released. Different from traditional wet-chemical synthesis,one unique feature of LAL is its resultant extreme high-temperature and high-pressure local environment for the nucleation and growth of nanomaterials, despite being performed at room temperature. This extreme condition can induce the atomization and ionization of the target materials and liquid molecules to incur different chemical reactions. The laser, liquid, liquid additive, and target can significantly alter the local environment in a broad range. Thus, different phases and shapes of nanomaterials are producible even from the same target. Through directly comparing the products of LAL of 13 kinds of chosen representative metals synthesized under different conditions, this review presents and discusses current understandings, challenging issues, and perspectives related to the diversity of LAL-products, which is willing to promote a deeper investigation and discussion on a clear clarification of the chemical reactions and particle nucleation/growth processes.