Supported nanostructured photocatalysts: the role of support-photocatalyst interactions

Abstract

Heterogeneous photocatalysis employing semiconductor oxide photocatalysts is a sustainable and promising method for environmental remediation and clean energy generation. In this context, nanostructured photocatalysts, with at least one dimension in the 1-100 nm size regime, have attracted ever-growing attention due to their unique and often enhanced sizedependent physicochemical properties. While their reduced size ensures enhanced photocatalytic performance, the same makes it difficult and time/energy-demanding to remove/recover such nanostructured photocatalysts from aqueous media. This fundamental limitation has paved the way towards developing supported nanophotocatalysts where the active photocatalytic nanostructures are coated on the surface of polymeric or inorganic support materials, often in a core@shell conformation. This arrangement solves the problem of photocatalysts' recovery for effective reuse or recycling and leads to improved and desired target properties due to specific photocatalyst-support interactions. While the enhanced physicochemical properties of supported photocatalysts have been widely studied in many target applications, the role of support-photocatalysts interactions in improving these properties remains unexplored. This review article provides an updated viewpoint on the photocatalyst-support interactions and the resulting unique physiochemical properties important for diverse photochemical applications and the design of practical devices. While exploring the properties of supported nanostructured metal oxide/ sulfides photocatalysts such as TiO 2 and MoS 2 , we also briefly discuss the common strategies employed to coat the active nanomaterials on the surface of different supports (organic/polymeric, inorganic, active, inert, and magnetic).

Designing Highly Photoactive Hybrid Aerogels for In-Flow Photocatalytic Contaminant Removal Using Silica-Coated Bacterial Nanocellulose Supports

“…48 The presence of a silica coating over the BC aerogel support apparently favors the formation of phase-pure anatase TiO 2 , which is consistent with previous studies reporting enhanced anatase stability for silicasupported titania nanophotocatalysts. 12,39,49 Finally, in accordance with XRF data, increasing the SiO 2 content in hybrid aerogel affects TiO 2 loading, as indicated by the decrease in relative intensity of the highlighted (grey) anatase diffraction peak at around 25°(101) in samples with higher silica loading.…”

“…This precise and selective coating methodology results in a three-dimensional structure which preserves the initial porosity of the starting BC aerogel membranes after coating with SiO 2 , a feature that is vital for the envisioned in-flow water decontamination applications. 39 In fact, the employed base-catalyzed sol−gel procedure favors the growth of highly branched, compact silica networks, 44 resulting in the formation of a compact SiO 2 layer constituted of protruded NPs preferentially deposited on BC fibrils via heterogeneous nucleation on abundant surface hydroxyl groups of nanocellulose networks. In order to evaluate the impact of silica interlayer on the properties of BC@SiO 2 membranes as functional supports for titania aerogel photocatalyst, we varied the amounts of water, base catalyst, and silicon alkoxide precursor (TEOS) to obtain hybrid aerogels with increasing SiO 2 loading/coverage of nanocellulose fibers, but without any significant loss in porosity of the BC@SiO 2 membranes.…”

“…14,15 Additionally, since the fate of nanomaterials and their impact on ecosystems and living beings are still little known, there is a growing environmental concern regarding their possible release into the environment. 16,17 Since these limitations are inherently related to the nanoscale nature of nanomaterials, anchoring or embedding them on/in macroscopic supports or substrates offers a viable and interesting option to design functional nanocomposite materials in suitable forms (membranes, thin film-coated surfaces/beads, and monolithic aerogels 15,18 ) for water treatment applications. Recently, photocatalytic aerogels, especially in monolithic form with macroscopic size and microscopic internal nanostructure, have been successfully used for environmental remediation and energy applications.…”

“…While the small size of photocatalyst NPs renders them with high specific surface area and better photocatalytic efficiencies, the same makes it difficult and time-/energy-consuming to separate such small NPs from colloidal suspension after use. Hence, the use of nanomaterials in particulate/suspension form for real-life applications of water purification or wastewater treatment becomes nearly impractical due to the operational, energy-related, and economic difficulties associated with the management and recovery of nanomaterials. , Additionally, since the fate of nanomaterials and their impact on ecosystems and living beings are still little known, there is a growing environmental concern regarding their possible release into the environment. , Since these limitations are inherently related to the nanoscale nature of nanomaterials, anchoring or embedding them on/in macroscopic supports or substrates offers a viable and interesting option to design functional nanocomposite materials in suitable forms (membranes, thin film-coated surfaces/beads, and monolithic aerogels , ) for water treatment applications.…”

“…On the other hand, silica-based materials have been found to exhibit high (photo)­stability and inertness. Moreover, the addition of silica to semiconductors has been found to improve the adsorptive, thermal, optical, and photocatalytic properties of semiconductors-silica nanocomposite systems. , The role of silica as excellent photocatalysts support is evident, for instance, from the superior photocatalytic performance of SiO 2 –TiO 2 nanocomposites compared to pure titania materials. ,,,, To prevent the possible photodegradation of BC by the TiO 2 in BC–TiO 2 composites and improve the structural properties of BC membranes and hence the overall photocatalytic performance of the system, we herein propose to coat BC membranes with a nanostructured silica interlayer using the conventional sol–gel method to obtain BC@SiO 2 membranes and then modify them with TiO 2 aerogel using an epoxide-driven sol–gel methods, , followed by hydrothermal crystallization/supercritical drying to obtain BC@SiO 2 /TiO 2 aerogel membranes. The inorganic silica interlayer serves as an inert, transparent barrier between the biopolymer (BC) matrix and TiO 2 aerogel, preventing possible photodegradation of BC nanofibrils and assisting in the adsorption of pollutant molecules.…”