Synthesis and characterization of TiO2-graphene heterostructured quantum dots by electrochemical process

Abstract

Titanium dioxide (TiO2) is a trendily attractive semiconductor owing to its optical and electrical properties within the UV-visible range. Nevertheless, limitations such as instability in the UV range and rapid recombination of photogenerated charge carriers leading to poor efficiency in photoactivity are major limiting factors that hold back the application of the materials on large scale. In order to tackle the stated issues, graphene quantum dots (GQDs), with their high carrier conductivity, UV-stability and thermal conductivity, can be used to improve TiO2’s flaws as optoelectronic materials. As a suitable edge transporter and modifier, GQDs can be grown as heterostructure well-bonded with TiO2 quantum dots. This material modification can lead to combined benefits of using TiO2 QDs’ preferable optoelectronic properties in UV-visible range and GQDs’ high conductivity and stability. This allows the synthesis of heterostructured quantum dots that can be tailored towards wide range of applications such as electron transport layer materials in perovskite solar cells or highly stable colloidal-based photocatalysts. In this study, TiO2/GQDs nanocomposites were synthesized using a solution-based electrochemical process with citric acid and potassium chloride (KCl) acting as electrolytes. Our proposed recipe yielded heterostructured QDs with average size of 3.44 nm well below the exciton Bohr radius of both TiO2 and graphene and hydrodynamic sizes around 45-59 nm with zeta potential in range of -24 to 30 mV. This yielded colloidal solution with stability and surface ion tunability based on KCl concentration with 0.3 M being the most stable recipe. Additionally, absorption band edge can also be tuned within the range of 2.8-3.9 eV which can be adjusted with concentration of KCl based on the desired applications.