Graphene Quantum Dot-TiO2 Photonic Crystal Films for Photocatalytic Applications

Abstract

Photonic crystal structuring has emerged as an advanced method to enhance solar light harvesting by metal oxide photocatalysts along with rational compositional modifications of the materials’ properties. In this work, surface functionalization of TiO2 photonic crystals by blue luminescent graphene quantum dots (GQDs), n–π* band at ca. 350 nm, is demonstrated as a facile, environmental benign method to promote photocatalytic activity by the combination of slow photon-assisted light trapping with GQD-TiO2 interfacial electron transfer. TiO2 inverse opal films fabricated by the co-assembly of polymer colloidal spheres with a hydrolyzed titania precursor were post-modified by impregnation in aqueous GQDs suspension without any structural distortion. Photonic band gap engineering by varying the inverse opal macropore size resulted in selective performance enhancement for both salicylic acid photocatalytic degradation and photocurrent generation under UV–VIS and visible light, when red-edge slow photons overlapped with the composite’s absorption edge, whereas stop band reflection was attenuated by the strong UVA absorbance of the GQD-TiO2 photonic films. Photoelectrochemical and photoluminescence measurements indicated that the observed improvement, which surpassed similarly modified benchmark mesoporous P25 TiO2 films, was further assisted by GQDs electron acceptor action and visible light activation to a lesser extent, leading to highly efficient photocatalytic films.

Visible Light Trapping against Charge Recombination in FeOx–TiO2 Photonic Crystal Photocatalysts

“…The hexagonally ordered macropores of the inverse opals structure were interconnected through smaller ones (dark areas within the large spherical voids) that form after calcination at the contact points of neighboring polymer spheres facilitating mass transfer in the pore network. Their mean diameter ( D ) determined by SEM, increased proportionally to the colloidal sphere size ( Table 1 ), while the obtained values were about 60% smaller than those of the templating spheres because of the persistent volume contraction of crystalline metal oxide inverse opals [ 33 , 60 ]. Cross-section SEM images revealed that the thickness of the inverse opal films was approximately 4 μm ( Figure 1 e), while that for the P25 film was approximately 2.2 μm ( Figure 1 f).…”

“…Films of 2 cm 2 area were initially stirred in vials containing 3 mL of 30 μΜ SA aqueous solution for 30 min under dark in order to reach adsorption-desorption equilibrium. The solution pH was fixed at 3 by dilute HCL in order to enhance SA adsorption on the TiO 2 films [ 33 ]. A 150 W Xe lamp was used as a UV–Vis light source along with a heat-reflective mirror (20CLVS-3, Newport, Irvine, CA, USA), while visible light was selected by a 400 nm cutoff filter.…”

“…Besides extending the optical path of incident photons, PC structures, the most common being inverse opals as well as periodically ordered alumina and GaN structures tailored by electrochemical anodization [ 21 , 22 , 23 ], provide a macroporous scaffold that along with the secondary mesoporosity of its inorganic skeleton lead to a network of interconnected macro-mesopores [ 24 ], which facilitate reactants adsorption and diffusion during the photocatalytic process [ 25 ]. Substantial research has been thus devoted to exploiting these advantageous characteristics in combination with materials’ compositional properties in order to develop visible light-activated (VLA) photonic photocatalysts [ 26 ], including coupling PCs with plasmonic [ 27 , 28 , 29 , 30 ] and graphene nanomaterials [ 31 , 32 , 33 ] as well as metal-oxide (MO) nanoclusters [ 34 , 35 , 36 ].…”

Novel Structures and Applications of Graphene-Based Semiconductor Photocatalysts: Faceted Particles, Photonic Crystals, Antimicrobial and Magnetic Properties

“…In recent years, the composites of PCs with graphene-based materials (G, GO, rGO) have been explored for numerous applications, such as switch [47], electronic and optoelectronic devices [48][49][50][51], sensors [52,53], surface-enhanced Raman scattering (SERS) [54], and photocatalysis [47,55,56], as exemplary shown in Table 1.…”

“…The fabrications of graphene-based PCs, where graphene-like materials (GO/rGO) act as co-catalysts, has been mostly carried out by immersing/dipping the IO PC into GO colloidal suspension with subsequent post-thermal treatment (calcination) [55,68,69,71]. On the other hand, the formation of graphene-like materials as the backbone material of IO PC requires at least three-step procedure i.e., (i) preparation of template (opal), (ii) infiltration of opal with targeted material, and (iii) the removal of sacrificial template.…”