Visible photodegradation of ibuprofen and 2,4-D in simulated waste water using sustainable metal free-hybrids based on carbon nitride and biochar

doi:10.1016/j.jenvman.2018.11.015

Journal of Environmental Management

Volume 231, 1 February 2019, Pages 1164-1175

https://doi.org/10.1016/j.jenvman.2018.11.015 Get rights and content

Highlights

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Metal free organic semiconductors based nano-assemblies as photocatalysts.
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Utilizing g-C₃N₄, acidified C₃N₄, PANI for designing efficient photocatalyst.
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Z-scheme mechanism-high spectral response and charge separation.
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Excellent photo-degradation of Ibuprofen and 2,4-D under artificial and solar light.
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Complete mineralization and no toxicity on human PBL cells.

Abstract

Rational designing of metal-free carbon nitride based photocatalysts can lead to an excellent optical response and a higher photocatalytic activity driven by visible and solar light. This combines green photocatalytic technology with greener materials prepared by facile approaches for environmental remediation. Herein we report utilization of star photocatalyst g-C₃N₄ (CN) to form highly efficient hetero-assemblies along with acidified g-C₃N₄ (ACN), polyaniline (PANI), reduced graphene oxide (RGO) and biochar. By use of these organic semiconductors we synthesize g-C₃N₄/ACN/RGO@Biochar (GARB), g-C₃N₄/PANI/RGO@Biochar (GPRB) and ACN/PANI/RGO@Biochar (APRB) nano-assemblies with different optical response and band edge positions for a better charge flow and reduced recombination of carriers. These synthesized catalysts were used for visible light powered degradation of 2,4-Dichlorophenoxy acetic acid (2,4-D) and ibuprofen (IBN). APRB performs the best and degrades 99.7% and 98.4% of 2,4-D and IBN (20 mg L⁻¹) under Xe lamp exposure in 50 min and retention of high activity in natural sunlight. Optical analysis, photoelectrochemical response and radical quenching studies show both hydroxyl and superoxide radical anions as major reactive species and a Z-scheme photocatalytic mechanism. RGO acts as an electron mediator and protects higher positioned bands of PANI and ACN in APRB for a remarkable photocatalytic activity for a metal free material. The degradation pathway was analyzed by LC-MS analysis and 42% and 40% total organic carbon was removed in 2 h for 2,4-D and IBN degradation respectively. The toxicity of degraded products was analyzed by analyzing viability of human peripheral blood cells with retaining of 99.1% cells.

Graphical abstract

Introduction

The revolutionary urbanization and industrialization for ever-increasing demand of uplifting quality standards of human life have ended up in environmental contamination and depletion of energy sources (Zeng et al., 2017). In addition the production of energy still relies heavily on water which is constrained by its availability and accessibility (Guerra and Reklaitis, 2018). Therefore, utilizing highly efficient, environmental friendly and green technology and materials are required for removal of various pollutants (Xu et al., 2017) and energy production. In recent years pharmaceuticals products have emerged as a menace. Their presence in water bodies is a substantial eco-toxicological threat for the environment as they increase drug resistance in bacteria (Ahmadi et al., 2017). Ibuprofen (IBN) is a nonsteroidal anti-inflammatory drug commonly used in muscular pain, migraine, tooth aches inflammation condition etc. (Khedr et al., 2017). IBN has been detected in the environment in the range 10 ng L⁻¹ to 169 μg L⁻¹ (Méndez-Arriaga et al., 2010). 2,4-Dichlorophenoxy acetic acid (2, 4-D) is a widely used herbicide which is highly soluble in water and has endocrine disrupting activities & cause chromosomal aberrations in human lymphocyte (Jaafarzadeh et al., 2017). Advanced oxidation processes have proven to be highly efficient for removal of pharmaceuticals from waste water (Kanakaraju et al., 2018). Many research groups have been working to develop greener materials derived from plants, biomass to utilize hemicellulose, activated carbon, black carbons, biochar etc. for pollution remediation (Yan et al., 2015; Zhang et al., 2011, 2014). Among these materials interest in biochar and based materials have increased because of applicability in soil and water treatment (Zhang et al., 2013). Biochars show extraordinary affinity for various contaminants with hydrophobic and specific interactions, have high functionality and no toxicity (Wang et al., 2017). They have been used to remove antibiotics by sorption as well as degradation by coupling with semiconductors (Kemmou et al., 2018; Zhu et al., 2018).

Metal-free photocatalysts have been explored for harnessing of visible/solar light for contaminant degradation and water splitting (Kumar et al., 2017b; Martha et al., 2013). Graphitic carbon nitride is the most researched metal free semiconductor owing to its moderate band gap (2.7 eV), non-toxicity, cost effectiveness (Kumar et al., 2018a) and high strength & stability (Anjum et al., 2018). The problem lies in energy conversion and electron-hole recombination. Thus band gap engineering is required for producing semi-conductor hetero-materials for solar energy conversion (Dhiman et al., 2017; Sharma et al., 2016a). Graphene based materials having 2-D honeycomb structure of sp² bonded carbon with few layer thick possesses wide application in the fields of adsorption, photocatalysis, solar batteries and hydrogen storage (Platero et al., 2017). Among conducting polymers polyaniline (PANI) has been extensively researched due to its unique band gap and high visible light absorption coefficient through its extended π-electron conjugated system (Sharma et al., 2015). Utilizing single semiconductors have their own limitations which can be overcome by formation of heterojunctions leading to improved spectrum capture and reduced recombination (Bhoi and Mishra, 2018; Kumar et al., 2017c). This experimental work focusses at designing of a highly optically active metal free hybrid photocatalyst which not only improves activity of graphitic carbon nitride but is also capable of competing with highly efficient metal based photocatalysts. In addition utilization of biochar from bio-wastes as a part of photocatalyst makes the synthesis as a complete greener approach.

Section snippets

Synthesis of g-C₃N₄ (CN), acidified g-C₃N₄ (ACN), biochar (BC) and GARB

The synthesis of CN and ACN is given in supplementary data. Synthesis of biochar from bio-waste (A brewery industry in Western Himalayan region, India) was done by same method as in our previous work (Kumar et al., 2017a). In a typical procedure 500 mg of graphene oxide (prepared by modified Hummer method) was suspended in 200 ml distilled water and sonicated for 30 min (Ultrasonic Frequency: 42000 Hz, timer: Digital timer with 5 cycles, Tank Material: Stainless Steel SUS304, Tank Capacity:

FTIR analysis

The FTIR spectrum for g-C₃N₄ (Fig. 2(a)) shows the presence of intense bands from 1200 to 1650 cm⁻¹ assigned to aromatic CN heterocycles and 1627, 1569 & 1409 cm⁻¹ for heptazine unit. The bands at 1318 and 1232 cm⁻¹ arise due to the stretching vibration of C−NH –C or N(C)₃ which is also supported by the broad band at 3139 cm⁻¹ due to the stretching mode of N−H bonds (Tian et al., 2014). For ACN, a red shift and broadening is observed. The peaks at 1618, 1395 and 1221 cm⁻¹ show a shift due to

Conclusion

In conclusion elaborative designed metal free nano-assemblies based on bare g-C₃N₄, acidified g-C₃N₄, polyaniline, RGO supported on biochar were synthesized by a simple approach. In comparison to single and binary catalysts, GARB, GPRB and APRB exhibit excellent photocatalytic activity for visible assisted degradation of IBN and 2,4-D. APRB leads to almost complete removal of both the pollutants IBN and 2,4-D in less than 60 min of exposure with retaining of higher activity in natural solar

Acknowledgments

The authors extend their appreciation to the Deanship of Scientific Research, King Saud University for funding this work through research group no. RG-1436-034.

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Research articleVisible photodegradation of ibuprofen and 2,4-D in simulated waste water using sustainable metal free-hybrids based on carbon nitride and biochar

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis of g-C3N4 (CN), acidified g-C3N4 (ACN), biochar (BC) and GARB

FTIR analysis

Conclusion

Acknowledgments

J. Environ. Manag.

Chem. Eng. J.

J. Mol. Liq.

J. Environ. Manag.

Chem. Eng. J.

Int. J. Hydrogen Energy

J. Clean. Prod.

Renew. Sustain. Energy Rev.

J. Photochem. Photobiol. A Chem.

J. Photochem. Photobiol. A Chem.

Separ. Purif. Technol.

Chemosphere

Water Res.

J. Environ. Manag.

J. Hazard. Mater.

Catal. Today

J. Photochem. Photobiol. A Chem.

Chem. Eng. J.

J. Clean. Prod.

Int. J. Biol. Macromol.

Water Res.

J. Hazard. Mater.

Water Res.

Appl. Surf. Sci.

J. Colloid Interface Sci.

J. Colloid Interface Sci.

Carbon

Research article
Visible photodegradation of ibuprofen and 2,4-D in simulated waste water using sustainable metal free-hybrids based on carbon nitride and biochar

Synthesis of g-C₃N₄ (CN), acidified g-C₃N₄ (ACN), biochar (BC) and GARB