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Efficient charge separation for a photocatalyst can be realized via addition of a co-catalyst, whereby most conventional techniques, i.e., deposition–precipitation, photoreduction, hydrothermal and vapour phase deposition result typically in surface loading effects. Moreover, the loading amount is deliberately kept nominal (below 10 wt%) as excessive loading causes both agglomeration and light blocking issues which limit the performance and stability of the photocatalyst. This work demonstrates one-pot in situ synthesis towards interdispersion and inclusion of a high concentration (Cu : TiO2 weight ratio > 1) of a Cu NP co-catalyst into TiO2 nanosheets without compromising its critical dispersivity and light absorption properties. The exceptional photocatalytic H2 performance of 16.1 ± 0.35 mmol g−1 h−1 stems from the embedment and confinement of the small Cu NPs within the TiO2 matrix which facilitates a shorter diffusion distance, thereby increasing the number of electrons available for catalytic reactions. Thus, this work highlights a facile approach towards optimal interfacing of the hybrid catalyst constituents to mitigate the limited interfacial contact and charge transfer challenges commonly faced in photocatalyst design.

Traditionally, porous carbon can be realized through chemical activation as well as templating with different materials for generation of hierarchical pores. However, the former method often results in the loss of the carbon’s initial structure, while the latter is known to be complex and requires additional procedures to remove the templates. This work demonstrates one-step activation-excavation approach towards simultaneous etching of hierarchical pores with the preservation of its hollow framework for enhanced volatile organic compounds (VOCs) adsorption and supercapacitance performance. The improvement in activity in both applications stems from the micropores, mesopores and hollow interior for containment, selectivity of larger adsorbents and enhanced transport diffusion respectively for VOCs adsorption. Similarly, the hierarchical pore sizes and hollow cavity in supercapacitors serve the purpose of increased electroactive sites, provides shorter diffusion pathway and facilitates ion diffusion for improved capacitive rate. Thus, this facile and effective approach of producing hollow interior and hierarchical pores carbon nanostructures is promising for bifunctional pollutant removal and energy storage solutions.

The performance of photocatalytic oxidation of volatile organic compounds (VOCs) generally depends on two properties: VOCs adsorption abilities as well as the degradation functionalities. In this work, a hybrid system of silicon dioxide (SiO2) and titanium dioxide (TiO2) was synthesized for enhanced degradation functionalities. The reasons for high demand of porous silica in the applications are attributed to the low cost, high surface area and the feasibility of obtaining various pore sizes. A simple aqueous-phase method was used to synthesize different structures of porous silica for VOC adsorption capabilities. Porous SiO2 rods of the highest surface area (1238 m2g-1) was chosen to incorporate with the TiO2 sheets for enhanced degradation. Hydrothermal TiO2 growth on SiO2 was optimized by varying the amount of precursors used. The synthesized materials were characterized with scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy and photocatalytic performance for VOC degradation under UV-LED illumination. The optimized SiO2rods@TiO2 sample showed enhancement of degrading up to 60 % in 120 min of degradation. Furthermore, CuO acts as an effective co-catalyst to enhance charge separation and the degradation performance was improved by loading the SiO2rods@TiO2 sample with CuO. A loading amount of 5% was found to be the optimum for enhanced degradation performance.

Absorbent materials such as activated carbon have been demonstrated to be very effective for the adsorption and removal of organic pollutants from the environment. However, this method of environmental remediation only allows the pollutant to be captured in the absorbent, instead of total decomposition into non-toxic end-products. This means that the absorbent material has to be disposed after one-time use, or additional steps has to be taken to clean the material before it can be reused. Motivated by this drawback, we have herein designed a hierarchical nanostructured composite material combining the adsorptive qualities of activated carbon with the photocatalytic activity of photoactive TiO2. However, contrary to existing literature, nano-sized activated carbon spheres are used instead of micron-sized spheres, and rather than TiO2 nanoparticles, thin and expansive 2D TiO2 nanosheets are synthesized. The combination of these 2 structures results in a flower-like 3D nanostructured monolithic composite material system capable of fast adsorption and complete degradation of environmental organic pollutants. The composite material was tested in the degradation of aqueous pollutants such as methyl orange dye and volatile organic compounds such as ethanol, methanol and formaldehyde. This synthesis effort highlights a highly effective material system that plays a pivotal role and holds great promise in commercial large scale cleaning operations.

Over the years, the exploration of inorganic chromogenic materials commonly interfaced with expensive noble metals has been limited, while the study of organic photochromic materials has proliferated. The key challenge lies in the optimization of inorganic materials’ constituents and structural design to achieve enhanced light–matter interaction chromism with performance commensurate with that of their organic counterparts. Here, we demonstrate a tailored inorganic transition metal cavity that boosts optically controlled reversible and repeatable chromism driven by a photocatalytic reaction. The solution-processable TiO2/CuO nanocomposite is endowed with a mesoporous cavity that is highly adept at performing self-regulating reversible photochromism under solar irradiation. The improved photoreactive chromism stems from the tailored critical structural parameters of the highly accessible mesoporous shell, reduced charge carrier diffusion length thin shell, and cavity enhanced optical field for photon–matter interactions. Consequently, the nanocomposite exhibits dual-functional photoregulated effects, i.e. photochromism mediated light transmittance modulation and rewritable printing/patterning. The nanocomposite offers high sensitivity, resulting in a short response time due to the efficient charge transfer, and such chromism effects are stable in the ambient environment. Furthermore, controlled switching of the chromism effects may be obtained simply by low-temperature heating. The concerted combination of inexpensive materials/production, low toxicity and a highly transparent noble metal-free inorganic nanocomposite renders chromogenic properties that will trigger a renewed interest in smart light-stimulus integrated technology.

Two-dimensional (2D) hydrated layered structures have emerged as a fascinating new class of materials for diversified surface mediated redox reactions. Here, a solution-processable 2D hydrated layered structure, Ni(OH)2 nanosheets with hollow TiO2 nanosphere composite has been designed to realize complementary electrochemical and catalysis reactions. The inherent 2D anisotropic lamellar hydrated framework of Ni(OH)2 contains interstitial spaces to promote efficient and reversible insertion/extraction of electrolyte ions without compromising its structural integrity. This translates to a fast switching speed and high stability valence change of metal ions that actively tunes the optical transmittance. Additionally, the Ni(OH)2 nanosheets synergistically play a co-catalyst role to enhance the photocatalytic degradation reactivity of TiO2 nanospheres. Correspondingly, the TiO2 nanospheres are composed of a porous thin shell that provides abundant active sites, distinct cavity diameter with enhanced light harvesting and improved reactant accessibility with a porous framework. Collectively, the nanocomposite is devised to exemplify a monolithically integrated multiple functionalities material system that unprecedentedly delivers photocatalytic degradation coupled electrochromism for environmental and energy conservations.