Original Research Paper
Oxygen-rich TiO2 decorated with C-Dots: Highly efficient visible-light-responsive photocatalysts in degradations of different contaminants

https://doi.org/10.1016/j.apt.2019.03.014Get rights and content

Highlights

  • Novel TiO2-peroxo/C-Dots photocatalysts as efficient photocatalysts are reported.

  • The TiO2-peroxo/C-Dots (0.75 mL) nanocomposite exhibited the highest activity.

  • Activity was 79.2-folds greater than TiO2 in RhB degradation under visible light.

  • The nanocomposite displayed substantial activity in degradations of different pollutants.

Abstract

Providing novel photocatalysts with high photocatalytic efficiency is of great significance. In the present work, hydrogen peroxide and carbon dots (C-Dots) were utilized to enhance the photocatalytic performance of TiO2 under visible light. The fabricated TiO2-peroxo/C-Dots photocatalysts were analyzed by XRD, HRTEM, SEM, EDX, BET, FT-IR, XPS, PL, UV–Vis DRS, EIS, and photocurrent density. Photocatalytic abilities of the nanocomposites were evaluated by photocatalytic removal of RhB, MO, MB, fuchsine, and Cr (VI) upon visible-light illumination. The results demonstrated that the binary nanocomposites exhibited remarkably enhanced photocatalytic activity compared with the TiO2 and TiO2-peroxo photocatalysts. The best photocatalytic performance was obtained using 0.75 mL of C-Dots, which was approximately 79.2, 17.1, 71.4, and 40.5 times higher than the pure TiO2 for degradations of RhB, MO, MB, and fuchsine, respectively. Furthermore, the TiO2-peroxo/C-Dots nanocomposites exhibited high stability in consecutive photocatalytic processes. Based on the results, the TiO2-peroxo/C-Dots photocatalyst is expected to become a promising photocatalyst for practical applications in water purification.

Introduction

Natural waters are primarily polluted by organic and inorganic contaminants, which have caused great damage to the environment and human health [1], [2], [3], [4]. Therefore, it is important to explore an effective and advanced method to minimize or neutralize the environmental harm of these pollutants. Semiconductor-based photocatalysis has been considered as one of the efficient methods to tackle environmental pollution and energy crises [5], [6], [7], [8], [9], [10]. As compared to other semiconductors, titanium dioxide (TiO2) plays a considerable role in the field of environmental protection applications, owing to its high oxidation ability, low cost, environmental-friendly nature, and photochemical stability [11], [12], [13], [14], [15], [16], [17], [18]. However, the photonic efficiency of TiO2 is poor under visible light, because it can only absorb UV light. To solve this drawback, various approaches have been proposed, like doping metals or non-metals to the structure of TiO2, dye photosensitization, and combining TiO2 with other semiconducting materials to form heterojunctions [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29].

Besides the above approaches, interaction of hydrogen peroxide (H2O2) with TiO2 to synthesize TiO2-peroxo is an effective approach to boost its photocatalytic performance under visible light. By H2O2 treatment, band gap energy of TiO2 is remarkably decreased, resulting in considerable absorption in visible region [30], [31], [32], [33]. Recently, carbon dots (C-Dots) as a carbon nanomaterial have attracted significant research attention in the photodegradation field, due to their excellent electronic, optical, and upconversion photoluminescence properties. C-Dots can suggest promising benefits in the photocatalytic systems by converting lower-energy lights to higher-energy lights, enabling more absorption of the visible spectrum of solar light [34], [35], [36], [37].

Based on this background, in this work, TiO2-peroxo/C-Dots photocatalysts were prepared by a simple procedure. Then, the fabricated photocatalysts were fully characterized and they revealed exceptional photocatalytic ability for removal of rhodamine B (RhB), methyl orange (MO), methylene (MB), fuchsine, and photoreduction of Cr (VI). The free radical quenching tests displayed that radical dotOH and radical dotO2 radicals have crucial role in the RhB degradation. The photoluminescence (PL) and photocurrent analyses were carried out to confirm the effective separation of charge carriers in the binary TiO2-peroxo/C-Dots photocatalysts. The reusability tests of the photocatalyst have also been performed. Eventually, a probable mechanism for the improved photocatalytic performance of the TiO2-peroxo/C-Dots photocatalysts was proposed.

Section snippets

Instruments

The detailed description for characterization methods included in the supporting information.

Fabrication of TiO2-peroxo

For synthesis of the TiO2-peroxo photocatalyst, 4 mL titanium (IV) butoxide (Loba Chemie, 99%) was added into 30 mL H2O2 (Loba Chemie, wt. 30%) solution (1 M) followed by 60 min of stirring. The obtained product was collected, washed by water and ethyl alcohol and dried. Then, the formed yellow solid was calcined at 400 °C for 120 min [31].

Fabrication of TiO2-peroxo/C-Dots

The C-Dots was synthesized according to a procedure described

Results and discussion

Crystalline structures of the as-prepared photocatalysts were explored by XRD measurements, as shown in Fig. 1. The diffraction angles of TiO2 and TiO2-peroxo samples can be related to the tetragonal structure of TiO2 (JCPDS file no. 04-0477) [31]. For the TiO2-peroxo/C-Dots nanocomposites, due to the low content and high dispersion of C-Dots over TiO2, no distinct characteristic peaks of C-Dots were observed [40].

To achieve the elemental compositions of the TiO2, TiO2-peroxo, and TiO2

Conclusions

Briefly, in this work, the TiO2-peroxo/C-Dots photocatalysts were fabricated by a facile procedure. The TiO2-peroxo/C-Dots (0.75 mL) nanocomposite showed the highest photocatalytic ability for degradations of RhB, MO, MB, and fuchsine and photoreduction Cr(VI), exceeding that of the pure TiO2 by a factor of 79.2, 17.1, 71.4, 40.5, and 21.8, and the TiO2-peroxo by a factor of 3.3, 3, 2.3, 1.81, and 1.77, respectively. The improved photoactivity of the well-designed binary nanocomposite was

Acknowledgment

The authors are very thankful for the financial support from University of Mohaghegh Ardabili, Iran.

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