Heterojunctions in Composite Photocatalysts

Abstract

Combining different light-absorbing materials for the formation of semiconductor heterojunctions is a very effective strategy for preparing highly active photocatalyst and photoelectrochemical systems. Moreover, the combination of solid state semiconductors with polymers or molecular absorbers expands the possible combinations of materials to alter light absorption and optimize charge carrier separation. In this chapter, different strategies to prepare such composites are presented, highlighting the necessity of intimate interfacial contact for optimum charge carrier transfer. Moreover, the most recent developments and improvements in the formation of heterojunctions and composite photocatalyst systems based on semiconductor solids are presented.

Amorphous and Crystalline Sodium Tantalate Composites for Photocatalytic Water Splitting

“…28,33 Therefore, two samples (0.25-NaTa and 4.0-NaTa) with mixed morphologies and phases were investigated in detail by high resolution transmission electron microscopy (HR-TEM). First, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 11 0.25-NaTa was examined as it is a mixture of amorphous sodium tantalate and crystalline NaTaO 3 nanoparticles (Figure 3a-b).…”

“…Composites of amorphous and crystalline samples or mixtures of different crystalline phases have proven to enhance the photocatalytic activity of samples toward water splitting. , Therefore, two samples (0.25-NaTa and 4.0-NaTa) with mixed morphologies and phases were investigated in detail by HR-TEM. First, 0.25-NaTa was examined as it is a mixture of amorphous sodium tantalate and crystalline NaTaO 3 nanoparticles (Figure a,b).…”

“…In this composite sample, the presence of both phases might increase the charge carrier separation as it is known for heterojunction materials and thus enhance the photocatalytic activity. 33 Similar amorphous−crystalline composite samples have been demonstrated to form heterojunctions and improve separation of photoexcited charges if the thickness of the amorphous region is small. 45−49 In our case, the amorphous matrix can reach distances of severalhundred nanometers; however, as it consists of a porous network, the minimum diffusion path for charge carriers through the amorphous matrix is only a few nanometers, as shown by the HR-TEM observation (Figures 3a,b and S6c,d).…”

High Surface Area SnO2–Ta2O5 Composite for Visible Light‐driven Photocatalytic Degradation of an Organic Dye

“…This increased in the photocatalytic activity of as‐prepared composite could be attributed to its higher surface area (Table ) compared to the other materials, which in turn could increase the surface active sites and facilitate the efficient charge separation during the photocatalytic process. Another possible explanation for the enhanced photocatalytic activity of the as‐prepared composite is the formation of heterostructure with high surface area, where Ta 2 O 5 and SnO 2 are expected to form a band edge overlap , which could reduce the recombination rate of electron‐hole pairs generated during the photocatalytic process, thus increasing its photocatalytic activity. Thus in these composites, the influence of surface area could also aid in controlling the rate of degradation as well as the amount of degraded product.…”

Layered Perovskite Nanofiber Heterojunctions with Tailored Diameter to Enhance Photocatalytic Water Splitting Performance

“…Recently, it was shown that by adjusting the synthesis conditions and precursor ratios, barium tantalate multicomponent heterojunctions could be easily obtained. , The construction of multiphase or multicomponent semiconductor heterojunctions is another very prominent strategy to improve photocatalytic activity by enhanced charge carrier separation. , Heterojunctions made of Ba 5 Ta 4 O 15 –Ba 3 Ta 5 O 15 and Ba 5 Ta 4 O 15 –Ba 3 Ta 5 O 15 –BaTa 2 O 6 therefore showed strongly improved performance in hydrogen production and water splitting compared to phase-pure Ba 5 Ta 4 O 15 . For the two-component heterojunction, laser flash photolysis experiments revealed the mechanism of enhanced activity, being most probably due to prolonged electron lifetimes by charge injection from the .…”