Defects play a pivotal role in the device performance of a photocatalytic, light-emitting, or photovoltaic system. Herein, graphitic carbon nitride (g-C 3 N 4 ) nanosheets are prepared at different calcination temperatures, and the evolution of defects in the system is studied by positron annihilation spectroscopy (PAS) and photoluminescence (PL) spectroscopy. Steady-state PL spectra show that free and defect-bound excitonic emission peaked at 2.78, 2.58, and 2.38 eV are dominant with above-band-gap excitation. Timeresolved PL studies reveal a significant enhancement of excitonic lifetime from 17.4 ns for free exciton to 27.4 ns in case of defect-bound exciton. We provide a direct correlation between the defects observed by PAS and those of the excitonic lifetime found from PL studies. Below-band-gap excitation activates defect emission, and it is characterized by a short carrier lifetime (∼0.14 ns). An excitation power-dependent PL study with 405 nm laser shows a progressive red shift and narrowing of the emission line. We have interpreted the different PL features with defect band filling of exciton, interplanar, intraplanar, interchain exciton migration, etc. These results are significant for tuning the optoelectronic properties of g-C 3 N 4 nanosheets and exploiting their applications in various emerging areas.

Thermotherapy is a widespread technique that provides relief for muscle spasms and joint injuries. A great deal of energy is used to heat the surrounding environment, and heat emitted by the human body is wasted on our surroundings. Herein, a woven Kevlar fiber (WKF)-based personal thermal management device was fabricated by directly growing vertical copper–nickel (Cu–Ni) nanowires (NWs) on the WKF surface using a hydrothermal method. The treated WKF was combined with reduced graphene oxide (rGO) dispersed in polydimethylsiloxane (PDMS) to form composites using vacuum-assisted resin transfer molding (VARTM). This WKF-based personal thermal management system contained a conductive network of metallic NWs and rGO that promoted effective Joule heating and reflected back the infrared (IR) radiation emitted by the human body. It thus behaved as a type of thermal insulation. The Cu–Ni NWs were synthesized with a tunable Ni layer on Cu core NWs to enhance the oxidation resistance of the Cu NWs. The combined effect of the NW networks and rGO enabled a surface temperature of 70 °C to be attained on application of 1.5 V to the composites. The Cu3Ni1–WKF/PDMS provided 43% more thermal insulation and higher IR reflectance than bare WKF/PDMS. The absorbed impact energy and tensile strength was highest for the Cu1Ni3- and rGO-integrated WKF/PDMS samples. Those Cu–Ni NWs having higher Ni contents displayed better mechanical properties and those with higher Cu contents showed higher Joule heating performance and IR reflectivity at a given rGO loading. The composite shows sufficient breathability and very high durability. The high flexibility of the composites and their ability to generate sufficient heat during various human motions ensures their suitability for wearable applications.

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The electrochemical intercalation and extraction of Al 3+ ion in anatase TiO 2 is illustrated in various aqueous electrolytes in an attempt to demonstrate the viability of TiO 2 as an anode material for rechargeable aqueous aluminum-ion batteries. It is well understood that the primary barrier for diffusion of Al 3+ ion in TiO 2 is the poor electronic conductivity of TiO 2 . It is revealed that a small fraction of graphene (<2 wt %) could induce ultrafast diffusion of Al 3+ ion in TiO 2 . Estimation shows that graphene remarkably enhances the Al 3+ ion diffusion coefficient in TiO 2 by 672 times. Discharge capacities in the range of 33−50 mAhg −1 are obtained at a high current rate of 6.25Ag −1 for graphene incorporated TiO 2 . It is also seen that the nature of electrolytes critically influences the Al 3+ ion insertion phenomenon. The possibility of reversible crystal phase transition of TiO 2 to aluminium titanate due to Al 3+ ion intercalation-extraction is also demonstrated for the first time.