A recyclable silver nanoparticles/graphene oxide nanoscroll composite photocatalyst

https://doi.org/10.1016/j.eti.2020.101210Get rights and content

Highlights

  • AgNPs/GO nanoscroll composites have open-ended nanoscroll structures.

  • AgNPs/GO nanoscroll composites were synthesized as a recyclable photocatalyst.

  • AgNPs/GO nanoscroll composites mineralize methylene blue to colorless within 10 min.

  • The nanoscroll composites show no decomposition after ten photocatalytic cycles.

Abstract

In this work, silver nanoparticles/graphene oxide nanoscroll composites (AgNPs/GO nanoscroll composites) with open-ended nanoscroll structures were synthesized as a recyclable photocatalyst. The open-ended nanoscroll structures provide sufficient space to prevent the AgNPs from oxidizing and aggregating, and the π-π continuous surface provides an abundance of pathways for AgNPs transfer during photodegradation. To demonstrate the recyclability of the synthesized photocatalytic composites, methylene blue aqueous solution was photodegraded under optimal conditions over ten consecutive photocatalytic cycles. The result shows that the AgNPs/GO nanoscroll composites are able to mineralize methylene blue to colorless within 10 min in each cycle, and no decomposition was detected after ten cycles. The AgNPs/GO nanoscroll composites could be used as a recyclable photocatalyst in wastewater treatment applications.

Introduction

With rapid economic growth and industrialization, the environmental pollution caused by organic and inorganic wastes, and hazardous metal has become an overwhelming problem worldwide (Chen et al., 2010, Linsebigler et al., 1995, Ye et al., 2012). Dyes are commonly used to color products in the textile industries ; however, most dye molecules used do not bind to fibers (Park and Choi, 2003, Teng et al., 2012). Many dyes are therefore released into the water system, resulting in harm to the environment as well as human and animal health (Cervantes et al., 2010, Clarke et al., 2010, Kar et al., 2009, Konstantinou and Albanis, 2004). Photocatalysis is considered as one of the most effective methods of removing such organic pollutants from wastewater (Alsohaimi et al., 2020, Bramhaiah et al., 2016, Chen et al., 2018, Khoa et al., 2015b, Liu et al., 2017, Wang et al., 2017). Recently, nanomaterials have been used as adsorbents in photocatalysis owing to their high surface area (Santhosh et al., 2016). Some nanoparticles, such as silver nanoparticles (AgNPs), exhibit brilliant colors, which have been found to depend on both the particle size and shape (Ratner et al., 2003). These magnificent colors achieved are the result from the nanoparticles size and shape which determines light absorption, and is caused by the localized surface plasmon resonance (LSPR) effect of the AgNPs (Cushing et al., 2012, Linic et al., 2011). On the other hand, AgNPs can be used as a photocatalyst for several reasons: (1) The conduction electrons of the AgNPs gain the irradiation energy, resulting in high energy electrons at the AgNPs surface which is desirable for activating molecules on the particles for chemical reactions; (2) The electrons drive the reactions on the photocatalysts, and the density of the conduction electrons at AgNPs surface is much higher than that of any semiconductors; (3) In a photocatalysis system, both light harvesting and the catalyzing reaction were occurred on the AgNPs, so it is easy for charge to transfer between the AgNPs and supports (Christopher et al., 2011, Zhang et al., 2012); (4) The AgNPs have much better affinity than semiconductors to many reactants, especially organic molecules. As a consequence of their properties, AgNPs are considered as one of the most promising nanomaterial catalysts (Chi et al., 2014, Rycenga et al., 2011, Wang et al., 2013, Zheng et al., 2013). However, agglomeration and oxidation limit their reuse in photocatalysis (Chen et al., 2019). To overcome these problems, suitable substrates such as polymers, metal oxides, and graphene materials are used to disperse the AgNPs by forming composite photocatalysts (Naik et al., 2011, Wang et al., 2016b, Zhang et al., 2011).

Graphene oxide (GO) is one of the suitable substrates used to adsorb dyes because it can improve the transfer rate of conduction band electrons and has a high surface area (Khoa et al., 2015a, Madhu et al., 2015, Wang et al., 2016a). In addition, GO has a large number of oxygen functional bonds that assist the dispersion of GO in water to form a stable suspension. Owing to these properties, GO can be functionalized and hybridized with AgNPs to produce excellent composites. Nevertheless, because GO has a two-dimensional flat structures, it does not prevent AgNPs from oxidizing, which limits the reuse of the composites for subsequent photocatalytic processes (Zhang et al., 2018). GO nanoscrolls, which form nanoscroll composites with AgNPs, offer better photocatalyst recyclability than GO. This is attributed to the one-dimensional nanoscroll structures that can wrap AgNPs to prevent them from oxidizing and provide sufficient space to prevent AgNPs from agglomerating. However, there have been few reports on the synthesis and properties of GO nanoscrolls combined with AgNPs.

In this work, considering the huge photocatalytic potential, the AgNPs are used as the photocatalyst for photodegradation of MB. Simultaneously, to reduce the negative impact of agglomeration of AgNPs, GO are used as the carrier and protective agent to prevent AgNPs from agglomeration and oxidation. In addition, in order to protect the AgNPs from oxidation in long-term photodegradation use, the two-dimensional GO sheets are rolled up to one-dimensional nanoscrolls. Therefore, silver nanoparticles/ graphene oxide nanoscroll composites (AgNPs/GO nanoscroll composites) were synthesized for use as a recyclable photocatalyst. The controlled variable method, degradation sample (GO, AgNPs, AgNPs/GO nanoscroll composites), bath ratio of sample to methylene blue (MB) solution (1:100, 1:200, 1:300), initial MB concentration (100 mg/L, 200 mg/L, 300 mg/L), and light source (UV light, natural sunlight), was used to obtain the optimal conditions for photodegradation. In addition, to demonstrate the recyclability of the AgNPs/GO nanoscroll composite photocatalyst, ten consecutive cycles under the optimal conditions were comprehensively studied.

Section snippets

Materials and reagents

The materials and reagents were described in our previous report (Li et al., 2020). Graphite flake (median 7–10 micron) was purchased from Alfa Aesar a Johnson Matthey Co., Ltd. Potassium permanganate, sulfuric acid, hydrochloric acid, hydrogen peroxide, silver nitrate (AgNO3), trisodium 2-hdroxypropane-1,2,3-tricarboxylate (Na3Ct) and 2-dimethylamino ethanol (DMEA) were all purchased from Wako Pure Chemical Co., Ltd. Methylene blue (MB) was obtained from Chroma. All the chemicals used for the

Optimization of photocatalysis conditions for the AgNPs/GO nanoscroll composites

The optimal photocatalytic conditions were established using the controlled variable method. Several experiments were carried out to study the influence of a variety of factors on the photocatalytic performance of the AgNPs/GO nanoscroll composites.

Conclusions

In conclusion, AgNPs/GO nanoscroll composites with a novel structure were synthesized for use as a recyclable photocatalyst. Ten consecutive cycles of MB mineralization were used to demonstrate the recyclable photocatalytic properties. The results show that under the optimal conditions (bath ratio of AgNPs/GO nanoscroll composites to MB of 1:100, initial MB concentration of 100 mg/L, and UV light irradiation), the nanoscroll composites can mineralize MB to colorless within 10 min in all cycles,

CRediT authorship contribution statement

Xiaojuan Li: Conceptualization, Methodology, Software, Data curation, Writing - original draft, Visualization, Investigation, Writing. Jun Natsuki: Supervision, Proofreading. Toshiaki Natsuki: Ensure that the descriptions are accurate and agreed by all authors.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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