The fabrication of highly responsive, rapid response/recovery and durable relative humidity (%RH) sensors that can precisely monitor humidity levels still remains a considerable challenge for realizing the next generation humidity sensing applications. Herein, we report a remarkably sensitive and rapid %RH sensor having a reversible response using a nanocasting route for synthesizing mesoporous g-CN (commonly known as g-CN). The 3D replicated cubic mesostructure provides a high surface area thereby increasing the adsorption, transmission of charge carriers and desorption of water molecules across the sensor surfaces. Owing to its unique structure, the mesoporous g-CN functionalized with well dispersed catalytic Ag nanoparticles exhibits excellent sensitivity in the 11-98% RH range while retaining high stability, negligible hysteresis and superior real time %RH detection performances. Compared to conventional resistive sensors based on metal oxides, a rapid response time (3 s) and recovery time (1.4 s) were observed in the 11-98% RH range. Such impressive features originate from the planar morphology of g-CN as well as unique physical affinity and favourable electronic band positions of this material that facilitate water adsorption and charge transportation. Mesoporous g-CN with Ag nanoparticles is demonstrated to provide an effective strategy in designing high performance %RH sensors and show great promise for utilization of mesoporous 2D layered materials in the Internet of Things and next generation humidity sensing applications.

The direct synthesis of copper selenide nanoparticles from the reaction of ditertiarybutyl selenide tBu2Se with copper(ii) trifluoroacetate Cu(TFA)2 under mild conditions is reported. The isolation of a molecular species during the course of this reaction, established as [Cu2(TFA)2(tBu2Se)3], by spectroscopic studies and single crystal X-ray structure analysis, confirmed that metal selenide NPs are formed via this intermediate species containing a reduced copper center. Extending this reaction in the presence of commercial TiO2 (P25) offered an easy synthesis of copper selenide-titania nanocomposites with different Cu/Ti ratios. These nanocomposites, well-characterized by powder XRD, STEM, TEM, BET, XPS, EDX and UV-Vis studies, were examined as photocatalysts for the degradation of formic acid (FA). The nCu2-xSe-TiO2 nanocomposites with low mol% of copper selenide, i.e. n = 0.1 and 0.3 mol%, displayed a superior catalytic activity over P25, which is an established benchmark for photocatalysis under UV light.