Visible-Light-Driven Photocatalytic H<inf>2</inf> Production Using Composites of Co-Al Layered Double Hydroxides and Graphene Derivatives Dolores G. Gil-Gavilán, Juan Amaro-Gahete, Daniel Cosano, Miguel Castillo-Rodríguez, Gustavo de Miguel, Dolores Esquivel, José R. Ruiz, and Francisco J. Romero-Salguero American Chemical Society (ACS) The direct conversion of solar energy into chemical energy represents an enormous challenge for current science. One of the commonly proposed photocatalytic systems is composed of a photosensitizer (PS) and a catalyst, together with a sacrificial electron donor (ED) when only the reduction of protons to H2 is addressed. Layered double hydroxides (LDH) have emerged as effective catalysts. Herein, two Co-Al LDH and their composites with graphene oxide (GO) or graphene quantum dots (GQD) have been prepared by coprecipitation and urea hydrolysis, which determined their structure and so their catalytic performance, giving H2 productions between 1409 and 8643 μmol g-1 using a ruthenium complex as PS and triethanolamine as ED at 450 nm. The influence of different factors, including the integration of both components, on their catalytic behavior, has been studied. The proper arrangement between the particles of both components seems to be the determining factor for achieving a synergistic interaction between LDH and GO or GQD. The novel Co-Al LDH composite with intercalated GQD achieved an outstanding catalytic efficiency (8643 μmol H2 g-1) and exhibited excellent reusability after 3 reaction cycles, thus representing an optimal integration between graphene materials and Co-Al LDH for visible light driven H2 photocatalytic production.
Zn-Cr Layered Double Hydroxides for Photocatalytic Transformation of CO<inf>2</inf> under Visible Light Irradiation: The Effect of the Metal Ratio and Interlayer Anion Dolores G. Gil-Gavilán, Daniel Cosano, Juan Amaro-Gahete, Miguel Castillo-Rodríguez, Dolores Esquivel, José R. Ruiz, and Francisco J. Romero-Salguero MDPI AG Carbon dioxide is the main gas responsible for the greenhouse effect. Over the last few years, the research focus of many studies has been to transform CO2 into valuable products (CO, HCOOH, HCHO, CH3OH and CH4), since it would contribute to mitigating global warming and environmental pollution. Layered double hydroxides (LDHs) are two-dimensional materials with high CO2 adsorption capacity and compositional flexibility with potential catalytic properties to be applied in CO2 reduction processes. Herein, Zn-Cr LDH-based materials with different metal ratio and interlayer anions, i.e., chloride (Cl−), graphene quantum dots (GQDs), sodium dodecyl sulfate (SDS) and sodium deoxycholate (SDC), have been prepared by a co-precipitation method and characterized by different techniques. The influence of the interlayer inorganic and organic anions and the metal ratio on the application of Zn-Cr LDHs as catalysts for the photocatalytic CO2 reduction reaction under visible light irradiation is unprecedentedly reported. The catalytic tests have been carried out with Ru(bpy)32+ as photosensitizer (PS) and triethanolamine as sacrificial electron donor (ED) at λ = 450 nm. All LDHs materials exhibited good photocatalytic activity towards CO. Among them, LDH3-SDC showed the best catalytic performance, achieving 10,977 µmol CO g−1 at 24 h under visible light irradiation with a CO selectivity of 88%. This study provides pertinent findings about the modified physicochemical features of Zn-Cr LDHs, such as particle size, surface area and the nature of the interlayer anion, and how they influence the catalytic activity in CO2 photoreduction.
Ru- and Ir-complex decorated periodic mesoporous organosilicas as sensitizers for artificial photosynthesis Raúl Rojas-Luna, Miguel Castillo-Rodríguez, José R. Ruiz, César Jiménez-Sanchidrián, Dolores Esquivel, and Francisco J. Romero-Salguero Royal Society of Chemistry (RSC) Novel artificial photosynthetic systems based on PMOs containing surface Ru- and Ir-complexes as photosensitizers and Pt nanoparticles as catalysts act as efficient heterogeneous photocatalysts in the hydrogen evolution reaction.
Realization of High Energy Density Sodium-Ion Hybrid Capacitors through Interface Engineering of Pseudocapacitive 3D-CoO-NrGO Hybrid Anodes Wenliang Feng, Venkata Sai Avvaru, Rudi Ruben Maça, Steven J. Hinder, Miguel Castillo Rodríguez, and Vinodkumar Etacheri American Chemical Society (ACS) Sodium-ion hybrid capacitors (SHCs) have attracted great attention owing to the improved power density and cycling stability in comparison with sodium-ion batteries. Nevertheless, the energy density (<100 Wh·kg-1) is usually limited by low specific capacity anodes (<150 mAh·g-1) and "kinetics mismatch" between the electrodes. Hence, we report a high energy density (153 Wh·kg-1) SHC based on a highly pseudocapacitive interface-engineered 3D-CoO-NrGO anode. This high-performance anode (445 mAh·g-1 @0.025 A·g-1, 135 mAh·g-1 @5.0 A·g-1) consists of CoO (∼6 nm) nanoparticles chemically bonded to the NrGO network through Co-O-C bonds. Exceptional pseudocapacitive charge storage (up to ∼81%) and capacity retention (∼80% after 5000 cycles) are also identified for this SHC. Excellent performance of the 3D-CoO-NrGO anode and SHC is owing to the synergistic effect of the CoO conversion reaction and pseudocapacitive sodium-ion storage induced by numerous Na2O/Co/NrGO nanointerfaces. Co-O-C bonds and the 3D microstructure facilitating efficient strain relaxation and charge-transfer correspondingly are also identified as vital factors accountable for the excellent electrochemical performance. The interface-engineering strategy demonstrated provides opportunities to design high-performance transition metal oxide-based anodes for advanced SHCs.
Mechanical behavior of in P Twinning Superlattice Nanowires Zhilin Liu, Ioannis Papadimitriou, Miguel Castillo-Rodríguez, Chuanyun Wang, Gustavo Esteban-Manzanares, Xiaoming Yuan, Hark H. Tan, Jon M. Molina-Aldareguía, and Javier Llorca American Chemical Society (ACS) Taper-free InP twinning superlattice (TSL) nanowires with an average twin spacing of ~ 13 nm were grown along the zinc-blende close-packed [111] direction using metalorganic vapor phase epitaxy. The mechanical properties and fracture mechanisms of individual InP TSL nanowires in tension were ascertained by means of in situ uniaxial tensile tests in a transmission electron microscope. The elastic modulus, failure strain and tensile strength along the [111] were determined. No evidence of inelastic deformation mechanisms was found before fracture, that took place in a brittle manner along the twin boundary. The experimental results were supported by molecular dynamics simulations of the tensile deformation of the nanowires, which also showed that the fracture of twinned nanowires occurred in the absence of inelastic deformation mechanisms by the propagation of a crack from the nanowire surface along the twin boundary.
Wear behavior of copper–graphite composites processed by field-assisted hot pressing Qian Liu, Miguel Castillo-Rodríguez, Antonio Galisteo, Roberto Guzmán de Villoria, and José Torralba MDPI AG Copper–graphite composites with 0–4 wt % graphite were fabricated by field-assisted hot pressing with the aim of studying the effect of graphite content on microhardness and tribological properties. Experimental results reveal that hardness decreases with the graphite content. Wear testing was carried out using a ball-on-disc tribometer with a normal load of 8 N at a constant sliding velocity of 0.16 m/s. The friction coefficient of composites decreases significantly from 0.92 to 0.29 with the increase in graphite content, resulting in a friction coefficient for the 4 wt % graphite composite that is 68.5% lower than pure copper. The wear rate first increases when the graphite content is 1 wt %; it then decreases as the graphite content is further increased until a certain critical threshold concentration of graphite, which seems to be around 3 wt %. Plastic deformation in conjunction with some oxidative wear is the wear mechanism observed in pure copper, while abrasive wear is the main wear mechanism in copper–graphite composites.