Sphere-rod-like Ag/AgCl@Fe2O3 Z-scheme heterojunction as photocatalysts for efficient degradation of tetracycline under visible light irradiation.

Integration of multi-functional components into one is urgent for creating a viable platform to improve photocatalytic efficiency for environmental treatment. Here, MIL-88B-NH2 (Fe) was firstly employed to capture Ag+ cation for the formation of AgCl@MIL-88B-NH2 (Fe), and then turned into the strongly coupled Ag/AgCl@Fe2O3 with sphere-rod-like structure. As prepared Z-scheme Ag/AgCl@Fe2O3 heterojunction exhibited outstanding photocatalytic performance of tetracycline (TC) with a removal efficiency of 94.9% and a reaction kinetics of 0.0272 min-1, superior to single Ag/AgCl or Fe2O3, which attributed to the broad light absorption range and accelerated electron-hole pair separation stemmed from the synergistic effect between surface plasmon resonance effect (SPR) of metal Ag and AgCl/Fe2O3 heterojunction. Meanwhile, Ag/AgCl@Fe2O3 was found to be highly catalytic in the degradation of TC even after consecutive runs. Moreover, active species trapping experiments combined with ESR techniques revealed that superoxide radical, hydroxyl radical, electron, and hole all were involved in photodegradation of TC process. Importantly, the degradation intermediate products of TC were revealed in depth by LC-MS, and a possible degradation pathway was further proposed. This work opens up new insights into the integration of functional composites for the construction of advanced photocatalysts applied in environmental purification.

Strongly Coupled Ag/Sn-SnO2 Nanosheets Toward CO2 Electroreduction to Pure HCOOH Solutions at Ampere-Level Current.

Electrocatalytic reduction of CO2 converts intermittent renewable electricity into value-added liquid products with an enticing prospect, but its practical application is hampered due to the lack of high-performance electrocatalysts. Herein, we elaborately design and develop strongly coupled nanosheets composed of Ag nanoparticles and Sn-SnO2 grains, designated as Ag/Sn-SnO2 nanosheets (NSs), which possess optimized electronic structure, high electrical conductivity, and more accessible sites. As a result, such a catalyst exhibits unprecedented catalytic performance toward CO2-to-formate conversion with near-unity faradaic efficiency (≥ 90%), ultrahigh partial current density (2,000 mA cm-2), and superior long-term stability (200 mA cm-2, 200 h), surpassing the reported catalysts of CO2 electroreduction to formate. Additionally, in situ attenuated total reflection-infrared spectra combined with theoretical calculations revealed that electron-enriched Sn sites on Ag/Sn-SnO2 NSs not only promote the formation of *OCHO and alleviate the energy barriers of *OCHO to *HCOOH, but also impede the desorption of H*. Notably, the Ag/Sn-SnO2 NSs as the cathode in a membrane electrode assembly with porous solid electrolyte layer reactor can continuously produce ~ 0.12 M pure HCOOH solution at 100 mA cm-2 over 200 h. This work may inspire further development of advanced electrocatalysts and innovative device systems for promoting practical application of producing liquid fuels from CO2.

Construction of graphene oxide-coated zinc tetraphenyporphyrin nanostructures for photocatalytic CO2 reduction to highly selective CH4 product.

The zinc-based photocatalysts for CO2 reduction have attracted increasing attention, however, usually exhibit low CO2-to-CH4 selectivity. Here, the graphene oxide (GO)-coated zinc tetraphenylporphyrin (ZnTPP/GO) nanocomposites are successfully synthesized through a simple method. It is found that with the increase of GO content, the crystallinity of ZnTPP nanocrystals enhances with the size decrease, and then the light absorption can easily match with the solar spectrum. The optimal ZnTPP/GO sample exhibits the CH4 evolution rate of 41.6 µmol g-1 h-1 and CH4 selectivity of >95%, which are higher than those of ZnTPP nanocrystals (7.8 µmol g-1 h-1 and 50.3%). The systematic characterizations confirm that the generation of axial coordinated ZnOC bonds between ZnTPP and GO plays a key role in the formation of ZnTPP/GO nanostructure and their synergic effect on photocatalytic CO2 reduction. The encapsulation of GO on ZnTPP nanocrystals not only promotes the CO2 adsorption, interfacial reaction, and stability, but also accelerates the separation of photoinduced carriers on ZnTPP (0.1 ps vs. 425.9 ps), the transportation from ZnTPP to GO (2.3 ps vs. 83.6 ps), and their final enrichment on GO. This work provides a new strategy to apply graphene and organic nanomaterials in artificial photosynthesis.

Defective MNiFeO (M = Cu, Zn, Co, Mn) NRs derived from cation-exchanged Fe2Ni-MOFs for catalytic nitroarene hydrogenation.

Catalytic hydrogenation reduction provides a potential route to detoxify nitro compounds. Spinel NiFe2O4 (NiFeO) serves as a natural abundance and low-cost catalyst but suffers from low catalytic activity due to poor redox nature and limited active sites. Herein, defective MNiFeO (M = Cu, Zn, Co, Mn) nanorods (NRs) were synthesized by pyrolysis of cation-exchanged Fe2Ni-MOFs. The introduction of M modified the electronic structure of NiFeO and thus accelerated the electron transfer and proton transport in the hydrogenation of nitro aromatics. CuNiFeO exhibited the highest catalytic activity with a turn frequency of 2.89 × 105h-1, giving 308- and 422-fold larger than that of NiFeO-Vo and NiFeO in the reduction of 4-nitrophenol (4-NP). CuNiFeO NRs also presented exceptional performances in the reduction of the other nitroarenes. The remarkable improvement in activity of mesoporous CuNiFeO may be attributed to its ternary composites, and increased oxygen vacancies. This work not only provides a simple route to constructing mesoporous MNiFeO NRs with oxygen vacancies, but also further discusses the effects of metal component and oxygen defects in the catalytic reduction of 4-NP.

Heterostructure of Semiconductors on Self-Supported Cuprous Phosphide Nanowires for Enhanced Overall Water Splitting.

Rational design, controllable synthesis, and an in-depth mechanism study of Cu-based bifunctional semiconductor heterostructures toward overall water splitting (OWS) are imperative but still face challenges. Herein, n-type iron oxide and p-type nickel phosphide and cobalt phosphide are respectively coupled with p-type cuprous phosphide nanowires on Cu foams via a general growth-phosphorization strategy. These self-supported semiconductor heterojunctions with different built-in potentials (EBI) are used as binder-free electrodes for OWS and exhibit significantly improved electrocatalytic activities compared to their counterparts. Among them, the heterostructure with the largest EBI of 1.57 V attains the smallest overpotential of 97 mV at 10 mA cm-2 for the hydrogen evolution reaction and 243 mV at 50 mA cm-2 for the oxygen evolution reaction in 1 M KOH. The corresponding two-electrode electrolyzer requires a cell voltage of 1.685 V at 50 mA cm-2 and shows admirable long-term stability at 100 mA cm-2 with a Faraday efficiency of around 98%. These promoted electrocatalytic performances originate from the enhanced active site, accelerated charge transfer, enlarged electrochemical active surface area, and synergy between different components at the heterointerface. This work represents a promising avenue to construct cost-efficient semiconductor heterostructures as bifunctional electrocatalysts applied to the sustainable energy industry.

Urchin-like hybrid nanostructures of CuOx/Fe2O3 from Cu-mediated pyrolysis of Fe-MOFs for catalytic reduction of organic pollutants.

MOFs have been widely used as templates to design and construct catalysis materials, such as LDH, metal oxides, and carbon. Herein, we developed a Cu-mediated pyrolysis protocol for the synthesis of urchin-like CuOx/Fe2O3 hybrid nanostructures using Fe-MOFs as the precursor. The hierarchical hybrids were composed of an inner CuOx-dispersed Fe2O3 octahedral matrix covered with radially grown Fe2O3 nanorods. This novel hierarchical hybrid nanostructure was generated likely due to the difference in the inward contraction rates between the Cu and Fe species during pyrolysis. Given the structural and compositional benefits, the urchin-like CuOx/Fe2O3 hybrids exhibited outstanding catalytic activity for the chemical reduction of 4-nitrophenol (4-NP) and dyes. Besides, CuOx/Fe2O3 was found to be highly catalytic in the reduction of 4-NP even after 30 consecutive runs, manifesting outstanding durability for continuous operation.

Assembly of Cobalt Layered Double Hydroxide on Cuprous Phosphide Nanowire with Strong Built-In Potential for Accelerated Overall Water Splitting.

Heterostructure plays an important role in boosting the overall water splitting (OWS) performance of nonprecious metal electrocatalysts. However, rational design and synthesis of semiconductor heterojunctions especially for Cu-based ones as efficient bifunctional electrocatalysts toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) still face challenges, and the in-depth study of catalytic mechanisms is urgently needed. Herein, n-type cobalt layered double hydroxide nanosheets are assembled on p-type cuprous phosphide nanowire to form p-n junction. This heterostructure with a strong built-in potential (EBI ) of 1.78 V provides enlarged electrochemical active surface area, enhanced active site, facilitated electron separation and transfer, and accelerated formation of superoxide radical. As expected, the heterogeneous electrocatalyst exhibits significantly improved activities for OWS, achieving an overpotential of 111 mV for HER and 221 mV for OER and an applied voltage of 1.575 V for OWS at 10 mA cm-2 in 1 m KOH. Moreover, the overpotentials are further decreased under visible light irradiation. This work represents a new insight into Cu-based catalysts toward OWS and an approach based on EBI to design semiconductor heterostructure promising for renewable energy applications.