Search

Among the many recently developed photo-catalytic materials, graphitic carbon nitride (g-C3N4) shows great promise as a catalytic material for water splitting, hydrogen generation, and related catalytic applications. Herein, synthesized bulk g-C3N4 is simply irradiated under a 35 fs pulse at mixed photon energies (800 nm and its second harmonic). g-C3N4 was synthesized from melamine following a facile thermal polymerization procedure. The prepared material was introduced, in an aqueous environment, to the femtosecond laser for various lengths of time. The treated material demonstrates a significant increase in surface area, relative to the untreated samples, indicating that irradiation is a successful method for exfoliation. The subsequent characterization reveals that the mixed irradiation process drives significant defect generation and sheet growth, which is not seen under 800 nm irradiation. Extended mixed irradiation results in 4 nm thick nanosheets with lateral dimensions 4× that of the bulk material. The treated material shows improved dye absorption/removal. This novel method of defect generation and nanosheet growth shows great potential as a g-C3N4 pre-treatment method for co-catalytic applications. Herein it is shown that femtosecond laser irradiation drives exfoliation beyond 100 nm particle sizes, and sheet-like morphologies under extended irradiation, which must be taken into account when using this method to improve material performance. [ABSTRACT FROM AUTHOR]

In this work the potential of employing electrophoretic deposition (EPD) for fabricating Li-ion battery electrodes without using binders and in particular eliminating volatile and toxic organic solvents such as n-methyl 2-pyrrolidone (NMP) is demonstrated. The paper in particular describes the successful application of the EPD method to fabrication of thick (>20 µm) nano-TiO2/carbon Li-ion intercalation anodes. The EPD system involves deposition of commercial P25 TiO2 nanoparticles and carbon black on aluminum foil from an isopropanol bath without making use of charging agents or other additives. Hetero-coagulation of TiCb and C particles in the isopropanol medium enabled their 80 V DC cathodic deposition into a well-adhered film with effective intermixing of active and conductive components. Electrochemical testing of the newly binder-free EPD-built electrodes revealed comparable film conductivity, polarization and charge storage capacity properties with the standard binder-based PVDF/NMP electrodes. Most importantly, the charge storage, cycling, and rate properties of the EPD-built electrodes were greatly enhanced by post-EPD sintering of the film at 450°C. The combined EPD-sintering route resulted in a superior conductive percolating network by promoting nanoscale film composition uniformity, inter-particle necking, and favorable porous structure for enhanced interfacing with the liquid electrolyte. The sintered EPD-built electrode exhibited almost 50% higher capacity retention than that of the standard binder-based electrode upon cycling. EPD with its inherent self-assembling functionality and its overall operational simplicity provides an advantageous and green Li-ion electrode fabrication alternative. [ABSTRACT FROM AUTHOR]

Among the many recently developed photo-catalytic materials, graphitic carbon nitride (g-C3N4) shows great promise as a catalytic material for water splitting, hydrogen generation, and related catalytic applications. Herein, synthesized bulk g-C3N4 is simply irradiated under a 35 fs pulse at mixed photon energies (800 nm and its second harmonic). g-C3N4 was synthesized from melamine following a facile thermal polymerization procedure. The prepared material was introduced, in an aqueous environment, to the femtosecond laser for various lengths of time. The treated material demonstrates a significant increase in surface area, relative to the untreated samples, indicating that irradiation is a successful method for exfoliation. The subsequent characterization reveals that the mixed irradiation process drives significant defect generation and sheet growth, which is not seen under 800 nm irradiation. Extended mixed irradiation results in 4 nm thick nanosheets with lateral dimensions 4× that of the bulk material. The treated material shows improved dye absorption/removal. This novel method of defect generation and nanosheet growth shows great potential as a g-C3N4 pre-treatment method for co-catalytic applications. Herein it is shown that femtosecond laser irradiation drives exfoliation beyond 100 nm particle sizes, and sheet-like morphologies under extended irradiation, which must be taken into account when using this method to improve material performance. [ABSTRACT FROM AUTHOR]

In this paper, electrophoretic deposition (EPD) is shown to promote nanoscale assembling of graphene oxide (GO) enabling the fabrication of highly homogeneous, robust, and capacity fade resistant composite titanium niobate (TiNb2O7, TNO)/rGO anodes upon reductive annealing. Control tests revealed that EPD is superior to conventional PVDF-based casting in maximizing the performance benefits from using reduced GO in Li-ion electrode fabrication as is the case of TNO that is plagued with conductivity and capacity fading problems. In this particular study, we show that there is a synergy developed between GO and EPD with the former (1) stabilizing the EPD suspension, (2) acting as a flexible binder net that affords mechanical integrity during the volume expansion of TNO, (3) serving as a conductive filler, and (4) contributing to Li-ion storage via pseudocapacitance. As a consequence, a superior percolation network is developed. Thus while both EPD- and PVDF- built TNO/rGO composite anodes exhibited high initial capacities (∼350 and 318 mA h g-1) at 0.5 C cycling, respectively, their cycling behaviour was quite different with the latter experiencing high internal polarization and extended degradation. Post-mortem PEEM-XANES analysis clearly demonstrated a highly homogeneous mesostructure in the case of the EPD-built TNO/rGO anode vs. a highly segregated and dis-jointed rGO and TNO component clustering in the PVDF-built electrode.