A transparent superhydrophilic self-cleaning nanocoating is fabricated and developed by hybridizing anatase TiO₂ with graphene sheets. In the hybrid preparation, ellipsoidal TiO₂ nanocrystals are grown exclusively over the graphene sheets, exposing high energy {001} and {010}/{100} facets. The hybrid is synthesized by a hydrothermally modified sol-gel method using CTAB (Cetyltrimethylammonium bromide) as the capping agent under an acidic of pH 3 and using very low weight percentage of graphene (0.1 wt %) with respect to as grown TiO₂. The synthesized samples are studied for its phase, crystallinity, exposed facets, and optical properties using Raman, TEM and DRS UV-Vis analyses. During the hydrothermal treatment, the graphene oxide sheets are reduced to graphene layers simultaneously on which in-situ growth of TiO₂ nanocrystals takes place. A close chemical contact between both TiO2 and graphene established is confirmed from XRD, XPS and FTIR analyses. The photocatalytic activity studied from degradation of Methylene blue dye is increased by graphene hybridization, with a change in kinetic rate constant k = 9.23 × 10-3 min-1 for pristine TiO₂ to 24.7× 10-3 min-1 for the hybrid. The fabricated nanocoating of the hybrid over a glass substrate showed about 94% transparency throughout the visible region and a superhydrophilic behavior with the water contact ~0o within 15 min of UV irradiation. The charge transfer mechanism by the reduced recombination rate in the hybrid is clearly investigated by PL spectra and TCSPC techniques.

Pristine anatase titanium dioxide (TiO₂) photocatalysts were prepared by a modified hydrothermal method using cetyltrimethylammonium bromide (CTAB) as the capping agent. The so-formed TiO₂ crystals showed superhydrophilic behavior in a short irradiation time span, without adopting any modifications to TiO₂ like doping or hybridizing with organic monolayers. At an optimum pH of 3, the CTAB molecules were effectively adhered to the high energy facets of TiO₂ favoring a crystal growth elongation in [001] direction leading to the exposure of high energy {101}/{100} and {001} facets. Variations in crystal morphology, size and exposing facets are investigated in detail using XRD, Raman and TEM, whereas the optical properties are studied using UV-Vis diffuse reflectance spectroscopy, PL and TSCPC techniques. The acetic acid acting as a bridging ligand attaching the Ti centers in a twisted conformation effectively led to the anatase phase of TiO₂. The shape and size of the CTAB micelles were greatly dependent on the pH of the reaction system, which in turn decided the exposure percentage of different facets. Anatase TiO₂ prepared at optimum pH 3 were ellipsoidal and showed 83% photocatalytic degradation (k = 9.23 × 10^-3 min^-1) of Methylene Blue as the model dye, and the water contact angle of 17⁰ under UV irradiation. When synthesis is repeated with double the quantity of water, TiO₂ shared ellipsoidal and cuboidal morphologies and were superhydrophilic showing contact angle of 9⁰ within 5 min UV irradiation, along with a superior photodegradation of 93% (k = 12.9 × 10^-3 min^-1).

Spatial charge separation is achieved by morphologically tuning TiO₂ nanomaterials along with graphene by a hydrothermally modified sol-gel synthetic route. Morphology engineered TiO₂ is constructed between nanocuboids with high energy {010}/{100} and {001}facets, and nanoellipsoids exposing low energy {101} facets. In situ grown titania hybridized with graphene (0.1% w/w) introduced chemical linkages as affirmed by XPS, Raman and FTIR studies. PL and TCSPC measurements greatly supported interfacial charge separation and reduced recombination rate in the hybrids. Photocatalytic studies determined that hybrids with TiO nanoellipsoids favoured hydrogen production as high as 18266.6 μL gm^-1L^-1hr^-1 under solar light illumination. While the hybrid with shared morphology of nanoellipsoids and nanocuboids for TiO₂ exhibited comparatively less H₂ production (13967 μL gm^-1L^-1hr^-1) but displayed extreme photoinduced wettability of ~0^o within 10 min of light irradiation. The divergence in the performance of morphologically tuned hybrids is explained using a plausible mechanism, assisted by photoconductivity and Hall-Effect measurements.

The bio-inspired nanotechnology of self-cleaning surfaces and coatings are nowadays being much attracted in the field of energy and environment because of the ever-increasing demand of uncontaminated, self-disinfected and hygienic surfaces. Such surfaces/coatings can be adopted on glass windows, automobile windshields, anti-fouling membranes, textiles, building construction materials, paints; on optoelectronic devices like solar panels, photochromic glasses, etc; in the food industry and for medical aids. This review gives a special emphasis to superhydrophilic self-cleaning surfaces. The mechanism of photocatalytic self-cleaning and superhydrophilicity of nano TiO2 based systems is carefully investigated. The photogenerated reactive oxygen species generated during photoexcitation of electrons from the valence band to the conduction band of TiO2 is responsible for its photocatalytic behaviour, anti-bacterial property and superhydrophilicity. Emphasis is given on various systems and methods that could enhance the self-cleaning behaviour of TiO2 in the solar spectrum since pristine TiO2 is only ultraviolet responsive. TiO2-semiconductor heterojunctions, hybrids of TiO2 with graphene and graphitic monolayers, tailoring the exposed crystal facets in TiO¬2, metal and non-metal doping and dye sensitization, attributing to visible light photocatalytic self-cleaning activity are focused in detail. Various techniques adopted for the synthesis and fabrication of superhydrophilic self-cleaning materials and coatings are discussed.

A two-step solvothermal synthesis was adopted to prepare AgXSe₂-TiO₂ (X = In, Bi) composites. DFT study of the pristine parent samples showed the formation of the hexagonal phase of AgBiSe2, and tetragonal phase of AgInSe₂ and TiO₂, which corroborated the experimentally synthesised structures. Both the AgBiSe2-TiO₂ and AgInSe₂-TiO₂ composites displayed enhanced visible light absorption and reduced band gap in the UV-DRS patterns. The XPS results exhibited a shift in binding energy values and the TEM results showed the formation of spherical nanoparticles of both AgBiSe2 and AgInSe2. The PL signals displayed delayed recombination of the photogenerated excitons. The as synthesised materials were studied for their photocatalytic efficiency, by hydrogen generation, degradation of doxycycline, and antimicrobial disinfection (E. coli and S. aureus). The composite samples illustrated more than 95 % degradation results within 180 min and showed 5 log reductions of bacterial strains within 30 min of light irradiation. The hydrogen production outcomes were significantly improved as the AgBiSe₂ and AgInSe₂ based composites illustrated 180-fold and 250-fold enhanced output compared to their parent samples. The enhanced photocatalytic efficiency displayed is attributed to the delayed charge recombination of the photogenerated electron-hole pairs in the AgXSe₂-TiO₂ interface. Formation of a p-n nano heterojunction for AgBiSe₂-TiO₂ and type II heterojunction for AgInSe₂-TiO₂ composite are explained.

A two-step solvothermal synthesis was adopted to prepare AgXSe₂-TiO₂ (X = In, Bi) composites. DFT study of the pristine parent samples showed the formation of the hexagonal phase of AgBiSe₂, and tetragonal phase of AgInSe₂ and TiO₂, which corroborated the experimentally synthesised structures. Both the AgBiSe₂-TiO₂ and AgInSe₂-TiO₂ composites displayed enhanced visible light absorption and reduced band gap in the UV-DRS patterns. The XPS results exhibited a shift in binding energy values and the TEM results showed the formation of spherical nanoparticles of both AgBiSe₂ and AgInSe₂. The PL signals displayed delayed recombination of the photogenerated excitons. The as synthesised materials were studied for their photocatalytic efficiency, by hydrogen generation, degradation of doxycycline, and antimicrobial disinfection (E. coli and S. aureus). The composite samples illustrated more than 95% degradation results within 180 min and showed 5 log reductions of bacterial strains within 30 min of light irradiation. The hydrogen production outcomes were significantly improved as the AgBiSe₂ and AgInSe₂ based composites illustrated 180-fold and 250-fold enhanced output compared to their parent samples. The enhanced photocatalytic efficiency displayed is attributed to the delayed charge recombination of the photogenerated electron-hole pairs in the AgXSe₂-TiO₂ interface. Formation of a p-n nano heterojunction for AgBiSe₂-TiO₂ and type II heterojunction for AgInSe₂-TiO₂ composite are explained.

The investigations on anthropogenic carbon dioxide (CO₂) capture and conversion play a vital role in eradicating global warming and the energy crisis. In this context, defect-engineered two-dimensional (2D) nanomaterials have received much attention in recent years. Herein, the significance of 2D nanomaterials such as graphene, transition metal dichalcogenides, hexagonal boron nitride, MXenes, graphitic carbon nitride, metal/covalent organic frameworks, nanoclays, borophenes, graphynes and green phosphorenes for CO₂ capture and conversion has been emphasized. Further, the intrinsic mechanism of CO₂ adsorption and conversion is discussed in detail. Theoretical and experimental studies among 2D materials highlight that N-doped porous adsorbents based on graphene and MXenes are more suitable for CO₂ adsorption applications. Also, more emphasis is given to outlining and discussing the role of various 2D nanomaterials and their hybrids as photocatalysts, electrocatalysts, photoelectrocatalysts, and thermocatalysts to transform CO₂ into valuable products. Although immense efforts are deployed in developing 2D catalysts for the conversion of CO₂, challenges such as agglomeration, poor yield, difficulties in analysing the 2D structures for catalytic factors, poor knowledge and in-depth understanding of the reaction mechanisms, high cost, etc. limit their large scale production and commercialization. More detailed theoretical and experimental investigations are required to develop 2D nanostructures with optimum properties for large-scale capture and conversion of CO₂.