In-situ fabrication of g-C3N4/MIL-68(In)-NH2 heterojunction composites with enhanced visible-light photocatalytic activity for degradation of ibuprofen

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Highlights

  • Novel g-C3N4/MIL-68(In)-NH2 heterojunction photocatalysts were synthesized for the degradation of ibuprofen.

  • Enhanced charge separation efficiency and visible light absorption were achieved.

  • Superior photocatalytic activity and adsorption capacity promoted the removal of ibuprofen.

  • The in-depth mechanism and characteristic degradation pathways were discussed in detail.

Abstract

For the first time, visible-light-driven g-C3N4/MIL-68(In)-NH2 heterojunction composites with high photocatalytic activity were prepared for the degradation of ibuprofen (IBP) using an in-situ solvothermal synthesis method assisted with ultrasonication. The composites achieved intensive visible-light absorption, enhanced separation efficiency of photogenerated carriers, and high adsorption capacity, thus achieving excellent photocatalytic degradation for IBP. Among all the composites, 10 wt% g-C3N4/MIL-68(In)-NH2 exhibited the maximum photocatalytic rate (0.01739 min−1), 19.28 and 2.00 times higher than those of g-C3N4 and MIL-68(In)-NH2, respectively. Moreover, the pH, ibuprofen concentration, and catalyst dosages played important roles both in photodegradation and adsorption. In addition, the photocatalytic mechanism was also elucidated, demonstrating that h+ was the main reactive species, followed by radical dotOH and radical dotO2 radicals, responsible for the degradation of IBP. Finally, seven aromatic intermediates of IBP were identified, and five possible degradation pathways were proposed, mainly involving hydroxylation, aldehyde oxidation, decarboxylation, and dehydrogenization reactions.

Introduction

In recent years, pharmaceutical drugs such as anti-inflammatories, antibiotics, and antidepressants, have been frequently detected in surface/underground water and wastewater with concentrations in the range of µg–ng/L [1], [2], [3]. These compounds have been categorized as emerging pollutants due to their high consumption, continuous release, biorefractory nature, potential hazard, and widespread distribution in environment [4], [5], [6], [7]. Ibuprofen (IBP), a widely used nonsteroidal anti-inflammatory drug with considerable production of a few kilotons per year in the world, has been recognized as a typical emerging pollutant [8], [9]. Although its toxicity and concentration are relatively low, IBP exhibits excellent stability, non-photolysis, and non-biodegradation, causing accumulation in aquatic environment and organism and thus poses severe threat to human health [10], [11], [12]. In addition, previous studies showed that conventional processes for wastewater plants were not efficient enough to remove IBP completely [2], [13], [14], [15]. Therefore, it is essential to develop new alternative technologies to solve the anti-inflammatory drug contamination problems in water.

Visible-light-driven photocatalysis, an environmentally friendly and highly effective method for the degradation of persistent organic pollutants, has been evaluated to treat IBP contaminated wastewater. It can convert IBP to biodegradable compounds, CO2, H2O, and inorganic ions by utilizing abundant solar energy [16], [17], [18], [19]. Extensive studies have been conducted to synthesize and optimize photocatalysts for the complete degradation of IBP [20], [21], [22], [23], [24]. However, the applications of these photocatalysts are rather limited by low solar energy conversion efficiency, easy photocorrosion, easy agglomeration, and unstable state in water. Consequently, it is necessary to explore novel photocatalysts without these shortcomings for IBP degradation.

Metal–organic frameworks (MOFs), constructed with organic ligands and metal-oxo clusters, have gained much attention owing to their widespread application prospect. It has been proved that MOFs can serve as light-sensitive semiconductors under solar illumination since the pioneering study on the photoactivity of MOF-5 [25]. Moreover, as a porous inorganic–organic hybrid material with infinite three-dimensional networks, MOFs possess stable crystalline structures, high pore volume, and large specific surface area, beneficial for overcoming the disadvantages of conventional photocatalysts, such as poor adsorption performance, low stability, and easy agglomeration [26], [27], [28]. Among all the MOFs synthesized in previous studies, MIL-68(In)-NH2, first reported by Farrusseng’s group, is considered to be a novel photocatalyst with excellent visible-light response [29]. According to Liang et al., MIL-68(In)-NH2 exhibited high photocatalytic activity for the reduction of Cr(VI) [30]. However, its application in the photocatalytic degradation of persistent organic pollutants is still limited by two key factors: (1) visible-light absorption edges and (2) separation efficiency of photogenerated electrons and holes. One of the most effective methods to overcome these limitations is to construct a heterojunction system by incorporating MOFs and semiconductors with well-matched band structures [31], [32], [33].

Thanks to appropriate energy levels and band structures, g-C3N4 and MOFs have been used to construct highly efficient heterojunction photocatalysts for wastewater treatment. Wang et al. [34] fabricated a novel g-C3N4/MIL-125(Ti) mesoporous photocatalyst using solvothermal method. Owing to the introduction of g-C3N4, the visible-light absorption range of g-C3N4/MIL-125(Ti) composites was significantly extended, leading to improved performance for Rhodamine B degradation. Lei et al. [35] successfully synthesized CNNSs/MIL-88B(Fe) hybrid nanocomposites by doping g-C3N4 nanosheets on the surface of MIL-88B(Fe). A high photocatalytic activity was achieved for the degradation of MB and reduction of Cr (VI). This can be attributed to the formed heterojunction. Yuan et al. [36] also reported an attractive heterojunction photocatalyst composed of g-C3N4 nanosheets and ZIF-8, which both enhanced the transfer rate of photogenerated carriers and the stability of materials. It can be concluded that doping g-C3N4 was a great way to improve the photocatalytic activity of parent materials, which successfully solved the problem that current photocatalyst materials were not effective enough to utilize solar energy for the degradation of contaminants. Meanwhile, high stability and efficient removal of pollutants with few catalysts, short operation time and low energy consumption were achieved, beneficial for practical application. Moreover, the complementarity and advantages of g-C3N4 and MOF were fully utilized. Combining highly photocatalytic activity with excellent adsorption capacity can greatly optimize the properties of catalysts and broaden their application fields [37]. Motivated by above studies, in this work, the novel visible-light-driven g-C3N4/MIL-68(In)-NH2 heterostructure composites with highly photocatalytic activity and adsorption capacity were developed. To the best of our knowledge, there have been no reports focus on the construction of type II heterojunction between g-C3N4 and MIL-68(In)-NH2, and this is the first study to report g-C3N4/MOF materials applied for the degradation of pharmaceutical and personal care products (PPCPs).

Herein, several g-C3N4/MIL-68(In)-NH2 composites were fabricated using a typical in-situ solvothermal method assisted with ultrasonication. Various characterization methods have been used to study the surface morphology, crystalline structure, chemical components, and electronic and optical properties of g-C3N4/MIL-68(In)-NH2. Furthermore, the g-C3N4/MIL-68(In)-NH2 was applied for the degradation of IBP under visible-light irradiation, and 93% removal rate was achieved in 120 min with few catalysts, low energy consumption, and no additional oxidants, which showed significant advantages comparable to previous reports [17], [38], [39]. Moreover, the effects of pH, IBP concentration and catalyst dosages on the photodegradation performance of composites were also discussed in detail. Finally, the stability and reusability of photocatalysts, possible photocatalytic mechanism, and degradation pathways of IBP were also explored to better understand the photocatalytic system. It can provide some references for practical application of materials and complete degradation of IBP.

Section snippets

Materials

Indium nitrate hydrate (In(NO3)3·xH2O, 99.99%, AR), 2-aminoterephthalic acid (H2BDC-NH2, 98.0%, AR), melamine (C3H6N6, 99.0%, AR), NN-dimethylformamide (DMF, 99.5%, AR), ibuprofen (C13H18O2, 98.0%, AR, CAS: 15687-27-1), and sodium sulfate (Na2SO4, 99%, AR) were purchased from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Sodium hydroxide (NaOH, 96.0%, AR), hydrochloric acid (HCl, 36%, AR), and ethylenediamine tetra acetic acid disodium (C10H14N2Na2O8·2H2O, 98%, AR) were supplied

X-ray diffraction (XRD) patterns

Fig. 1 shows the XRD patterns of as-synthesized samples. The diffraction peaks of MIL-68(In)-NH2 are consistent with those reported previously, indicating high crystallinity of materials [40]. The XRD pattern of g-C3N4 shows two typical diffraction peaks at 13.1° and 27.5°, corresponding to the interlayer stacking of g-C3N4 and stacking of conjugated aromatic system, respectively [41]. More importantly, the main characteristic peaks of parental MIL-68(In)-NH2 appeared in all the XRD patterns of

Conclusions

In summary, g-C3N4/MIL-68(In)-NH2 heterostructure composites were synthesized for the first time and applied to the photodegradation of IBP under visible-light irradiation. With the construction of the heterojunction at the interface between g-C3N4 and MIL-68(In)-NH2, significant increase in the photocatalytic activity of composites was achieved. Under the optimal experimental conditions, g-C3N4/MIL-68(In)-NH2-3 showed the highest degradation ratio (93%) and TOC removal efficiency (70%) towards

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 work was financed by the Social Science and Technology Development Project of Dongguan (No. 20185071631595), the NSF of China (No. 21976060), Fundamental Research Funds for the Central Universities (D2192900), and Applied Science and Development Project of Guangdong Province (No. 2016B020240005).

References (75)

  • N.B. Mohd Zanuri et al.

    Assessing the impact of diclofenac, ibuprofen and sildenafil citrate (Viagra®) on the fertilisation biology of broadcast spawning marine invertebrates

    Mar. Environ. Res.

    (2017)
  • M. Hijosa-Valsero et al.

    Assessment of full-scale natural systems for the removal of PPCPs from wastewater in small communities

    Water Res.

    (2010)
  • Y. Luo et al.

    A review on the occurrence of micropollutants in the aquatic environment and their fate and removal during wastewater treatment

    Sci. Total Environ.

    (2014)
  • Q. Sun et al.

    Seasonal variation in the occurrence and removal of pharmaceuticals and personal care products in a wastewater treatment plant in Xiamen, China

    J. Hazard. Mater.

    (2014)
  • D. Awfa et al.

    Photodegradation of pharmaceuticals and personal care products in water treatment using carbonaceous-TiO2 composites: a critical review of recent literature

    Water Res.

    (2018)
  • W. Huang et al.

    Integration of plasmonic effect into spindle-shaped MIL-88A(Fe): steering charge flow for enhanced visible-light photocatalytic degradation of ibuprofen

    Chem. Eng. J.

    (2018)
  • N. Liu et al.

    In-situ fabrication of needle-shaped MIL-53(Fe) with 1T-MoS2 and study on its enhanced photocatalytic mechanism of ibuprofen

    Chem. Eng. J.

    (2019)
  • M. Jiménez-Salcedo et al.

    Photocatalytic degradation of ibuprofen in water using TiO2/UV and g-C3N4/visible light: study of intermediate degradation products by liquid chromatography coupled to high-resolution mass spectrometry

    Chemosphere

    (2019)
  • Y. Gu et al.

    Adsorption and photocatalytic removal of Ibuprofen by activated carbon impregnated with TiO2 by UV–Vis monitoring

    Chemosphere

    (2019)
  • N. Jallouli et al.

    Heterogeneous photocatalytic degradation of ibuprofen in ultrapure water, municipal and pharmaceutical industry wastewaters using a TiO2/UV-LED system

    Chem. Eng. J.

    (2018)
  • R. Akbarzadeh et al.

    One-pot hydrothermal synthesis of g-C3N4/Ag/AgCl/BiVO4 micro-flower composite for the visible light degradation of ibuprofen

    Chem. Eng. J.

    (2018)
  • M. Akkari et al.

    ZnO/sepiolite heterostructured materials for solar photocatalytic degradation of pharmaceuticals in wastewater

    Appl. Clay Sci.

    (2018)
  • J. Choina et al.

    The influence of the textural properties of ZnO nanoparticles on adsorption and photocatalytic remediation of water from pharmaceuticals

    Catal. Today

    (2015)
  • J.L.C. Rowsell et al.

    Metal–organic frameworks: a new class of porous materials

    Microporous Mesoporous Mater.

    (2004)
  • R. Liang et al.

    NH2-mediated indium metal–organic framework as a novel visible-light-driven photocatalyst for reduction of the aqueous Cr(VI)

    Appl. Catal. B

    (2015)
  • Y. Jiao et al.

    A novel MoS2 quantum dots (QDs) decorated Z-scheme g-C3N4 nanosheet/N-doped carbon dots heterostructure photocatalyst for photocatalytic hydrogen evolution

    Appl. Catal. B

    (2019)
  • M. Lan et al.

    Fabrication of porous Pt-doping heterojunctions by using bimetallic MOF template for photocatalytic hydrogen generation

    Nano Energy

    (2017)
  • Y. Zhang et al.

    Porous Co3O4/CuO hollow polyhedral nanocages derived from metal-organic frameworks with heterojunctions as efficient photocatalytic water oxidation catalysts

    Appl. Catal. B

    (2016)
  • H. Wang et al.

    Synthesis and applications of novel graphitic carbon nitride/metal-organic frameworks mesoporous photocatalyst for dyes removal

    Appl. Catal. B

    (2015)
  • D. Yuan et al.

    Graphite carbon nitride nanosheets decorated with ZIF-8 nanoparticles: effects of the preparation method and their special hybrid structures on the photocatalytic performance

    J. Alloys Compd.

    (2018)
  • Y. Luo et al.

    Synergistic adsorption-photocatalysis processes of graphitic carbon nitrate (g-C3N4) for contaminant removal: kinetics, models, and mechanisms

    Chem. Eng. J.

    (2019)
  • V. Bhatia et al.

    Transition metal doped TiO2 mediated photocatalytic degradation of anti-inflammatory drug under solar irradiations

    J. Environ. Chem. Eng.

    (2016)
  • L. Wu et al.

    Amino-modified MIL-68(In) with enhanced hydrogen and carbon dioxide sorption enthalpy

    Microporous Mesoporous Mater.

    (2012)
  • L. Ye et al.

    Facets coupling of BiOBr-g-C3N4 composite photocatalyst for enhanced visible-light-driven photocatalytic activity

    Appl. Catal. B

    (2013)
  • W. Huang et al.

    Metal organic framework g-C3N4/MIL-53(Fe) heterojunctions with enhanced photocatalytic activity for Cr(VI) reduction under visible light

    Appl. Surf. Sci.

    (2017)
  • Y. Lv et al.

    Removal of p-arsanilic acid by an amino-functionalized indium-based metal–organic framework: adsorption behavior and synergetic mechanism

    Chem. Eng. J.

    (2018)
  • Y. Zhang et al.

    Visible light photocatalytic degradation of MB using UiO-66/g-C3N4 heterojunction nanocatalyst

    Chemosphere

    (2018)
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