Highly Active TiO2 Photocatalysts for Hydrogen Production through a Combination of Commercial TiO2 Material Selection and Platinum Co-Catalyst Deposition Using a Colloidal Approach with Green Reductants

Michael Schwarze,Riny Yolandha Parapat,Minoo Tasbihi,Ha Uyen Do,Edith Mawunya Kutorglo,Charly Klingbeil

doi:10.3390/catal11091027

Abstract

In this contribution, four different commercial TiO2 catalysts (P25, P90, PC105, and PC500) were screened for the photocatalytic production of hydrogen using ethanol as the sacrificial agent. The physico-chemical properties of the TiO2 powders were characterized by using different methods. The photocatalysts mainly vary in the ratio of anatase and rutile phases, and in the surface area. It was found that the photocatalytic activity is governed by the surface area of the photocatalyst. Pure TiO2,PC500 showed the best performance, and in comparison to P25, the activity was more than twenty times higher due to its high surface area of about 270 m2 g−1. For further improvement of the photocatalytic activity, platinum nanoparticles (PtNPs) were immobilized onto TiO2,PC500 using two methods: a colloidal approach and a photodeposition method. For the reduction of the platinum salt precursor in the colloidal approach, different green reducing agents were used in comparison to ascorbic acid. The obtained platinum nanoparticles using natural reductants showed a higher photocatalytic activity due to the formation of smaller nanoparticles, as proven by transmission electron microscopy (TEM). The highest activity was obtained when mangosteen was used as the green reducing agent. Compared to ascorbic acid as a classical reducing agent, the photocatalytic activity of the Pt@TiO2,PC500 prepared with mangosteen was about 2–3 times higher in comparison to other as-prepared photocatalysts. The Pt@TiO2,PC500 catalyst was further studied under different operating conditions, such as catalyst and sacrificial agent concentration.

Highlights

Hydrogen is the most important clean energy source able to solve the increasing concern of the declining fossil fuel reserves and environmental pollution
bandgap energy (BGE) is about (3.2 ± 0.1) eV, and UV light is required for photocatalytic experiments, which was provided by the 300 W Xe lamp
From the commercially available TiO2 catalysts that were investigated in this contribution for photocatalytic hydrogen production, PC500 showed the best photocatalytic performance

Summary

Introduction

Hydrogen is the most important clean energy source able to solve the increasing concern of the declining fossil fuel reserves and environmental pollution. In 1972, Akira Fujishima and Kenichi Honda, for the first time, performed artificial photosynthesis to produce chemical energy from light energy [7] They generated hydrogen in a photoelectrochemical setup with titanium dioxide (TiO2) as the photocatalyst. TiO2 was capable of using light to promote the chemical reaction After this groundbreaking discovery, photocatalysis became an important research field. As it is known that for water reduction, platinum nanoparticles (PtNPs) are usually deposited onto the surface of the semiconductor to increase the activity, the second goal of this contribution was to study the PtNPs’ loading in more detail. Based on our earlier experience in the preparation of supported catalysts [23,24,25], a colloidal approach was used to deposit PtNPs onto the surface of TiO2 This approach was compared with the photodeposition technique that is usually applied in photocatalysis for co-catalyst loading [26]. The immobilization route and experimental conditions have an enormous impact on the formation of PtNPs, as it has been reported by several researchers [27,28,29,30,31]

Methods

Results

Conclusion