Biomolecule-assisted solvothermal synthesis of 3D hierarchical Cu₂FeSnS₄ microspheres with enhanced photocatalytic activity

Highlights

• Cu₂FeSnS₄ microspheres were prepared by the biomolecule-assisted solvothermal method.

• Cu₂FeSnS₄ microspheres are composed by stannite nanosheets with thickness of 100 nm.

• The 3D hierarchical CFTS microspheres showed high visible light photocatalytic property.

Abstract

In this work, we developed a novel environmentally friendly strategy toward solvothermal synthesis of 3D hierarchical Cu₂FeSnS₄ microspheres with the utilization of l-cystine, an amino acid, as a coordination agent and sulfur donor. The crystal structure, surface morphology and microstructure of the as-prepared products were investigated. The results showed that the 3D hierarchical Cu₂FeSnS₄ microspheres were composed of stannite nanosheets, and the average thickness of nanosheets was 100 nm. Moreover, the 3D hierarchical Cu₂FeSnS₄ exhibited high efficiency in the photodegradation of RhB under visible light illumination, suggesting a promising candidate for treatment of organic pollutants in waste water.

Introduction

In recent years, the environmental pollution has forced people to develop green and efficient technologies for the sustainable development of human environment. Organic pollutant in waste water is a serious threat to the environment. Therefore, to deal with the increasingly severe environment crisis, it is pressing need and great significance to research high-efficient and low-cost materials to removal these pollutants. Recently, photocatalysis using effective semiconductors has become a promising route to degrade organic pollutants [1]. Based on this purpose, various types of semiconducting materials, such as CdTe/CdSe, Cu(In_xGa_1−x)Se₂ (CIGS), etc., have been extensively studied [2], [3]. However, due to the limited availability of indium and gallium and the toxicity of cadmium, it is considerable interesting to develop inexpensive, non-toxic, earth-abundant photocatalytic materials [4], [5]. Over the past years, scientists have been trying their best to find some materials consisted of only earth-abundant elements and retain the similar structure to CIGSS. Hence, a class of quaternary I₂–II–IV–VI₄ chalcogenides including Cu₂ZnSnS₄ (CZTS), Cu₂FeSnS₄ (CFTS) and other related chemical compounds are of great importance and interest due to similar crystal structure to CIGSS and earth-abundant composition [6]. Among them, CZTS have been extensively studied due to their direct band gaps of about 1.4–1.5 eV and high absorption coefficients (>10⁴ cm⁻¹) [7]. However, it is remains rare about the investigation on CFTS, another possible earth-abundant alternative to CIGSS.

CFTS is environmentally benign and cheap to fabricate due to the abundance of elements such as Cu, Fe, Sn, and S in nature [8]. Moreover, its suitable optical band gap (1.2–1.5 eV) and nontoxic constituents have attracted increasing attention [5]. Various methods have been used to prepare CFTS including solution-based method [5], [9], microwave nonaqueous synthesis method [10], spray pyrolysis [11], thermal decomposition [12], ultrasound-assisted microwave irradiation [13], solvothermal/hydrothermal method [14], [15], [16], etc. As an important solution-based chemical process, the solvothermal method has been extensively used to prepare various materials for its low temperature, simplicity and high yield. To the best of authors’ knowledge, there are no reports on the biomolecule-assisted solvothermal synthesis of CFTS. Here, we describe a green synthetic route to prepare 3D hierarchical CFTS microspheres by biomolecule-assisted approach, where l-cystine is used as a reducing agent and sulfur donor. It can effectively avoid the environmental and health risks when using sulfur, Na₂S, thiourea, and dimethyl sulfoxide as the sulfur source to fabricate such composites [17]. Furthermore, the structure, morphology, composition and optical property of as-synthesized CFTS particles are investigated. More importantly, the photocatalytic activity of the as-prepared 3D hierarchical CFTS is evaluated for the degradation of RhB solution under visible light illumination.