Stable construction of layered reduced grapheme oxide/copper sulfide composites on cellulose fibers with hyperbranched polyamide-amine for efficient photocatalytic degradation of organic dyes

Highlights

• A novel CuS-based photocatalytic composite paper is prepared.

• The load of reduced graphene oxide on fibers relies on hyperbranched polyamide-amine.

• Hyperbranched polyamide-amine grafted on fibers induces uniform growth of CuS.

• Reduced graphene oxide inhibits the recombination of photogenerated carriers in CuS.

• The composite paper exhibited high photocatalytic activity and good reusability.

Abstract

The use of semiconductor-based photocatalysts to degrade organic dyes in water is receiving more and more attention. However, there are still some problems in practical applications, such as high photogenerated carrier recombination rate, difficulty in recovery, and poor reusability. In this study, reduced graphene oxide (rGO)/copper sulfide (CuS) was loaded onto a dialdehyde cellulose fiber (DACF) with the help of hyperbranched polyamide-amine (HPAMAM) to construct a photocatalytic composite paper (DACF/HPAMAM/rGO/CuS paper). Based on the results, HPAMAM was bonded to DACF and rGO via CN and amide bond, and it could act as a nanoreactor to induce uniform and stable growth of CuS. The photocatalytic activity of the as-prepared DACF/HPAMAM/rGO/CuS paper in the degradation of rhodamine B was about 2.7 times that of the composite paper without HPAMAM and rGO (DACF/CuS paper). Such a high performance could be attributed to the improved charge separation efficiency and the stable composite structure of rGO/CuS in the composite paper. DACF/HPAMAM/rGO/CuS paper was also able to demonstrate excellent stability and reusability, which makes it a promising photocatalyst. This work provides a novel strategy for preparing highly efficient and stable photocatalytic composite paper for degradation of organic dyes.

Introduction

Water contamination directly threatens human health, and it is receiving more and more attention (Alsbaiee et al., 2016). Organic dyes with good chemical stability and low biodegradability are a kind of pollutants in wastewater that are difficult to treat by traditional physicochemical or biochemical methods. Therefore, many technologies have been developed to treat organic dyes in water, such as extraction, adsorption, photocatalysis, membrane separation, and Fenton reagent method (Yu et al., 2019; Shi et al., 2018; Nguyen et al., 2020; Dutta et al., 2018). Among them, the use of semiconductor-based photocatalysts for photocatalytic degradation of organic dyes has the advantages of low cost and high efficiency (Maeda, 2011; Liu et al., 2018; Zhu et al., 2017). Under light excitation, the electrons (e-) generated in the conduction band (CB) and the holes (h+) generated in the valence band (VB) would participate in the redox reaction, leading to the degradation of organic dyes. However, due to the high recombination rate of photogenerated carriers, only a few remaining electrons and holes participate in oxidation and/or reduction reactions (Legrini et al., 1993). Therefore, seeking a strategy that can effectively separate photogenerated carriers is particularly important for improving the photocatalytic efficiency of semiconductor catalysts (Di et al., 2018; Cai et al., 2020; Xia et al., 2018; Wang et al., 2019a, b; Ahmadi et al., 2017).

Carbon materials have become a research hotspot in many fields because of their excellent physicochemical properties (Cen et al., 2020; Wang et al., 2017a; Payan et al., 2018). The strong electron-trapping ability of carbon nanomaterials can effectively inhibit the recombination of photogenerated electron-hole pairs in semiconductor photocatalyst (Jiang et al., 2018; Wang et al., 2017b; Gao et al., 2019; Di et al., 2019). On the other hand, carbon nanomaterials can also improve light utilization efficiency. Therefore, carbon nanomaterials are considered as an effective modifier to improve the photocatalytic performance of semiconductor catalysts.

Copper sulfide (CuS) have received more and more attention in the fields of lithium ion batteries, solar cells, supercapacitors, and photocatalysis due to their excellent optical and electronic properties (Li et al., 2019a,b; Xiao et al., 2018; Hu et al., 2016). The CuS is expected to replace traditional TiO₂ and ZnO as an alternative semiconductor photocatalyst because of its narrow band gap (Yi et al., 2019; Wang et al., 2015). However, the photogenerated carrier recombination rate of CuS is still very high in the absence of electron capture materials. The use of carbon nanomaterials to support CuS has proven to be an effective strategy to circumvent this drawback (Basu et al., 2014; Cai et al., 2019; De et al., 2017; Basu et al., 2016).

Reduced graphene oxide (rGO) possesses a strong electron transfer capability and a large surface area, which has been used to support semiconductor catalysts to improve photocatalytic performance (Nethravathi et al., 2009). With the combination of rGO and CuS, charge equilibration would change the Fermi level, and the photogenerated electrons would be transferred by rGO (Gao et al., 2011). In this way, rGO can improve the photocatalytic ability of CuS (Saranya et al., 2015). Saranya et al. (2015) reported that a hydrothermally synthesized rGO/CuS composite degraded methylene blue with visible light. The rGO/CuS composites prepared by sonochemical method were also reported (Shi et al., 2014). However, there are still some problems in practical applications of rGO/CuS composite photocatalyst, such as poor reusability and difficult in recovery (Chen et al., 2019; Dong et al., 2019; Zhou et al., 2019). Anchoring composite photocatalyst on a substrate is an effective way to overcome these problems (Komeily‐Nia et al., 2019). In this work, rGO/CuS is loaded on cellulose fibers to prepare a photocatalytic composite paper. But a linker is still needed to graft rGO onto cellulose fibers and induce uniform and stable growth of CuS.

Hyperbranched polymer possesses a highly branched molecular structure and numerous of terminal functional groups, showing the advantages of low viscosity, low molecular entanglement, high reactivity, etc. (Konkolewicz et al., 2011; Voit and Lederer, 2009; Gao and Yan, 2004). Furthermore, the terminal functional group of the hyperbranched polymer facilitates its grafting in the composite system (Ratna, 2008; DeCarli et al., 2005; Wong et al., 2004). On the other hand, the steric hindrance caused by the highly branched structure of hyperbranched polymers can provide a stable growth place for nanoparticles (Cao et al., 2015). Hyperbranched polyamide-amine (HPAMAM) possesses a spheroid-like branched molecular structure and numbers of terminal amino groups (Rehim et al., 2011). HPAMAM can be connected to the dialdehyde cellulose fiber (DACF) and rGO through the bonding of CN and amide bond. In this case, HPAMAM acts as a linker that can graft rGO onto the cellulose fibers. More importantly, HPAMAM can also be used as a growth template and stabilizer to ensure the stable particle size and uniform distribution of CuS on the cellulose fibers.

In this study, rGO/CuS was loaded on cellulose fibers with the help of HPAMAM to construct a photocatalytic composite paper for the degradation of organic dyes in water. The effects of HPAMAM on the stability and uniformity of the rGO/CuS loaded on the cellulose fibers are investigated. Furthermore, the synergistic photocatalysis effect of rGO/CuS on cellulose fibers is analyzed in this work.