**4.3 Photocatalytic study of PENQ: TiO2 nanosystem**

Semiconductor photocatalysis experiments were performed by manufactured PENQ: TiO2 systems i.e. PT 5, 10 & 17 mmol from freshly prepared H2S gas. **Figure 5** shows the band structure and of H2S gas splitting in presence of UV light. Total hydrogen produced is 36,456 μmol/h/g for PT-5 nanosystem which is higher than PT-10 and 17 catalysts. As compared to TiO2 which is the best photocatalyst, this system produces four times higher hydrogen. 0.25 M KOH at pH 12.5, H2S splitting follows the as showed mechanism, hydrosulfide HSˉ ions (1). This system absorbs the light and produces electron and holes (2). Here holes (h+ VB) are responsible for oxidation HSˉ ion in to disulfide ion (S2 2−), taking a proton from HSˉ ion (3). Reduction faiths by using electrons to give hydrogen (4).

$$\mathrm{H\_{z}\mathrm{S}\,\mathrm{gas}} + \mathrm{OH^{-}} \leftrightarrow \mathrm{HS^{-}} + \mathrm{Water} \,(\mathrm{H\_{z}O}) \tag{1}$$

$$\text{Semiconductor photometry PENQ} : \text{TiO}\_2 \leftrightarrow \text{h}^\* \text{VB} + \text{e}^- \text{CB} \tag{2}$$

$$\text{Oxidation process}: 2\text{HS}^{-} + 2\text{h}^{\*}\text{VB} \leftrightarrow \text{S}\_{\text{z}}{}^{2-} + 2\text{H}^{\*}\tag{3}$$

$$\text{Reduction process}: 2\text{H}^\* + 2\text{e}^-\\\text{CB} \leftrightarrow \text{H}\_z \tag{4}$$

There is no any hydrogen generation was observed without catalyst and without light experiment; this proves that the hydrogen produced is because of PENQ: TiO2 photocatalyst.

#### **Figure 5.**

*The band structures and photocatalytic activity of PENQ: TiO2 hybrid nanosystem. Reproduced by copyright permission from the Royal Society of Chemistry.*
