Synthesis of PANi nanoarrays anchored on 2D BiOCl nanoplates for photodegradation of Congo Red in visible light region
Graphical abstract
Introduction
Environmental pollution with natural contaminants such as antibiotics, organic dyes, and pesticides has become a challenging task due to their carcinogenic and toxic effects on human and organisms [1], [2], [3]. Because of increasing daily usage of Congo Red (CR) in different industries including textile, printing, leather, paper, pulp, and cosmetic, remediation of the colored effluents is regarded as a solution to these environmental problems [4]. The mutagenic nature of these effluents impedes their treatment by physical and biological approaches [5]. Degradation of naphthalene and benzene rings of CR cannot apply with ordinary methods. Moreover, because of its aromatic structure, CR possesses high physiochemical, thermal, and optical stability [6].
Various techniques like biodegradation [7], adsorption [8], [9], ozonation, photocatalytic degradation, physiochemical treatment, catalytic reduction, and coagulation/flocculation are reported for treatment of dyes [10]. Advanced oxidation processes (AOPs) have drawn considerable attention in recent decades and be more useful for the oxidation of organic pollutants [11]. Despite the economic effectiveness of several adsorbents over CR removal, CR is not degraded by adsorbents and just transferred from liquid phase to solid phase. Therefore, the implementation of AOPs and among them light-driven photocatalytic processes for its high energy and environmental efficiency [12].
Nowadays, tremendous researches have focused on the design and development of innovative, efficient, and cost-effective approaches for remediation of wastewaters [13]. Because of the light-driven photocatalytic system is activated at the visible region (can be sunlight at large scales) and no additional reagent or chemical added to the CR solution, make it a great choice for degradation of this pollutant. Recently, bismuth-based compounds, specially BiOX (X = Cl, Br, I) have been received great attention in photocatalytic degradation of water pollutants [14], [15]. As a key V–VI–VII ternary semiconductor compounds, all BiOX have a tetragonal PbFCl-type structure, a layered structure described by [Bi2O2] sheets inserted by double sheets of halogen atoms [16]. The high photocatalytic activities of BiOX were mostly related to the indirect optical transition and their open crystalline structures. The first one means that the excited electron has to trip a certain distance emitted to the valence band (VB), which decreases the recombination likelihood of the excited electron and hole [17]. Several researchers have reported that nanostructured BiOCl compared to TiO2 displays the higher photocatalytic degradation performance under irradiation of visible light [18], [19], [20]. Furthermore, some dye molecules, including Rhodamine B can easily adsorb on the BiOCl surface, and under irradiation of visible light can be further degraded due to the dye sensitization phenomenon [21]. On the other hand, due to the determining role of morphology and the size of BiOCl particles on its photocatalytic performance, many approaches have been investigated for the synthesis of BiOCl with various morphologies such as solvothermal [22], precipitation [23], the reverse microemulsion route [24], the molecular precursor route [25], calcination [26], microwave irradiation [27], and hydrolysis [21]. Besides its significant photocatalytic activity, the overall photocatalytic efficiency of BiOCl still needs to be improved. In this regard, some modification approaches have been used, including co-catalyst use [28], [29], doping [30], [31], coupling [32], sensitization [33], graphene use [34], and making defects [35], [36]. Also, the conductive polymers including π-conjugated electron systems including polyaniline (PANi), polythiophene, polypyrrole, and their derivatives indicated the great encouraging in photocatalytic processes thanks to their attractive features including broad absorption in the visible light region and excellent stability [37], [38]. Besides, PANi is relatively cheap with simple synthesis approach in comparison with doped noble metals. Some reports depict the mixture of conductive polymers and some semiconductors to advance their photocatalytic performance as sensitization agents. Wang et al. [39] have reported the modification of BiOCl by PANi via chemisorption approach. The obtained PANi/BiOCl photocatalyst declared many plates of BiOCl with anchored PANi particles on their surface. The main morphological difference between the nanocomposites synthesized here with the earlier one reported by Wang by al. one is the creation of PANi nanoarrays by in-situ polymerization approach compared to nanoparticles of PANi attached on the surface of BiOCl sheets via chemisorption method. Therefore, we can consider the improvement in synthesis approach and morphological features of PANi/BiOCl to its enhanced performance. In another study, a multifunctional Ni0.5Zn0.5Fe2O4@PANi modified BiOCl was developed by Tanwar et al. [40] as highly effective and visible light-driven photocatalyst in the degradation of four toxic dyes. In that composite, the ferrite and PANi components absorb photons to create electron-hole pairs. This group in another work [41] prepared PANi/Fe0 doped BiOCl by chemisorption of PANi/Fe0 fibers on BiOCl plates. The nanocomposite showed 1.62 eV decrease in the estimated bandgap value compared to pure BiOCl with improved photocatalytic performance in the removal of CR under irradiation of visible light. However, in prior works, morphology control of PANi on BiOCl substrate has not been addressed, which may reduce the synergistic effects of two components. Hence, the construction of specially structured composites of BiOCl and PANi, which allows highly efficient utilization of PANi, remains a challenge.
In the present work, as shown in Scheme 1, we employed a novel two-step approach for the fabrication of PANi/BiOCl photocatalyst. For this means, firstly, 2D BiOCl sheets were synthesized by a hydrothermal approach then the in-situ oxidative polymerization of aniline monomer was performed in the existence of them to create PANi nanoarrays on their surface. The obtained PANi/BiOCl nanocomposite showed well-arranged nanoarrays of PANi on 2D BiOCl sheets surface and showed remarkable photocatalytic activity compared to previously reported work [39] in the degradation of CR under visible light irradiation.
Section snippets
Materials
The bismuth(III) nitrate pentahydrate (Bi(NO3)3.5H2O), sodium chloride (NaCl), ammonium persulfate ((NH4)2S2O8), hydrochloric acid (HCl), aniline (C6H5NH2), ethanol (C2H5OH), and KCl were all in analytical grade and purchased from Merck. The reagents were utilized as received without further purification. The distilled and deionized water was used during experiments.
Synthesis of 2D BiOCl sheets
The 2D BiOCl layers were synthesized as described elsewhere [42]. In brief, 1.94 g Bi(NO3)3·5 H2O was dissolved in 100 mL
Characterization of PANi/BiOCl photocatalysts
Fig. 1a indicates the XRD patterns of BiOCl and a set of PANi/BiOCl photocatalysts with 1, 5, 7, and 9 wt% of PANi. The XRD pattern of hydrothermally synthesized BiOCl is inconsistent with standard tetragonal structure (JCPDS 01-073-2060). The key diffraction peaks appear at 2θ’s of 11.98°, 24.10°, 25.40°, 33.45°, 34.40°, 36.50°, 41.51°, 46.52°, 49.6°, 55.70°, 58.41°, 61.33°, 75.43°, and 77.32° which correspond to the (0 0 1), (0 0 2), (1 0 1), (1 1 0), (1 1 1), (0 0 3), (1 1 2), (2 0 0), (1 1
Conclusions
In conclusion, we developed a new approach to synthesis 2D BiOCl sheets decorated by PANi nanoarrays as an efficient visible light driven photocatalyst for the removal of CR. The characterization techniques showed the effective growth and attachment of PANi nanoarrays on 2D BiOCl sheets which enhanced the active surface area and light-absorbing behavior, especially in the visible region. Almost 83.5% of CR at 10 mg L–1 was removed by 5 mg of 5 wt% loading of PANi/BiOCl within 60 min were the
Conflict of interest
There are no conflicts to declare.
Acknowledgments
The authors would like to acknowledge the University of Tabriz for support of this research.
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