Biocompatible FeOOH-Carbon quantum dots nanocomposites for gaseous NOx removal under visible light: Improved charge separation and High selectivity

doi:10.1016/j.jhazmat.2018.04.071

Journal of Hazardous Materials

Volume 354, 15 July 2018, Pages 54-62

https://doi.org/10.1016/j.jhazmat.2018.04.071 Get rights and content

Highlights

•
The fabricated CQDs/FeOOH nanocomposites showed enhanced NO removal activity.
•
Generation of toxic NO2 intermediates was inhibited over the nanocomposites.
•
Charge separation and transfer efficiency were improved by CQDs addition.
•
DFT calculations elucidated that the electron migration rate was enhanced.
•
NO removal mechanism was proposed based on detection of the reactive oxygen species.

Abstract

Development of biocompatible photocatalysts with improved charge separation and high selectivity is essential for effective removal of air pollutants. Iron-containing catalysts have attracted extensive attention due to their low-toxicity and high natural abundance. Here, carbon quantum dots (CQDs) modified FeOOH nanocomposites fabricated using a facile hydrothermal route showed enhanced NO removal efficiency (22%) compared to pure FeOOH. Moreover, generation of toxic NO₂ intermediates was significantly inhibited using the nanocomposites, demonstrating high selectivity for final nitrate formation. Photo-electrochemical results showed that both charge separation and transfer efficiency were significantly improved by CQDs addition, and the lifetime of photo-generated carriers was increased eventually. Density functional theory calculations further elucidated that the suppressed recombination of photo-induced electron-hole pairs was due to enhanced electron migration from the FeOOH to CQDs. A NO degradation mechanism was proposed based on detection of the reactive oxygen species using electron paramagnetic spectroscopy. In addition, the nanocomposite showed good biocompatibility and low cytotoxity, ensuring minimal environmental impact for potential application in large-scale.

Graphical abstract

Introduction

High concentrations of nitrogen oxides (NO_x) in the atmosphere contribute to environmental problems, such as acid rain and photochemical smog [[1], [2], [3]]. Hence, it is necessary to develop effective measures to control NO_x concentrations. Semiconductor photocatalysis offers an appealing route to remove NO_x at ambient concentration [4,5]. However, the development of economically feasible and eco-friendly photocatalysts with high efficiency remains a challenge.

Iron-containing catalysts have attracted extensive attention for NO_x removal as they have low toxicity, eco-friendliness, and high abundance in the Earth’s crust [[6], [7], [8], [9]]. Among the reported catalysts, iron (III) hydroxide (FeOOH) has been investigated for environmental pollution control due to its favorable band gap energy (∼2.6 eV) allowing visible light activation [10]. Unfortunately, FeOOH usually suffers from severe charge recombination due to inherently poor electrical conductivity, which greatly hinders broad application [11,12]. Therefore, many studies have focused on optimizing charge migration in FeOOH by constructing heterostructures with FeOOH and other materials. Wang et al. fabricated interwoven Co₃O₄-carbon@FeOOH hollow polyhedrons; the optimized composition and structure showed significant enhancement of the electrochemical properties [13]. Recently, Li et al. designed FeOOH/CeO₂ and FeOOH/Co/FeOOH hetero-layered nanotube arrays for the oxygen evolution reaction; the unique hybrid structure resulted in low energy barriers of intermediates and low mass-transfer resistance, enhancing the catalytic reaction [14,15]. Moreover, electron acceptors are important for fast transfer of the photo-generated electrons, realizing effective light utilization and high quantum yields [[16], [17], [18]]. For example, H₂O₂ was ingeniously introduced as an electron acceptor into the precursor solution in the presence of FeOOH to improve the photocatalytic activity [19]; H₂O₂ efficiently trapped electrons and increased the generation of hydroxyl radicals. Various high-conductivity materials, such as Au, CNT, and rGO, can be coupled with FeOOH to enhance the photocatalytic activity for pollutant degradation [[20], [21], [22], [23]].

The conjugated π structures of carbon quantum dots (CQDs) make them excellent electron transporters and acceptors [24], while the up-converted photoluminescence (UCPL) effect allows them to absorb solar radiation over a wide range of wavelengths (ultraviolet to infrared). In CQDs/TiO₂ composite photocatalysts, the CQDs convert visible or infrared light to shorter wavelengths via the UCPL effect and enhance electron transfer along specific directions [25,26]. Recently, various CQDs-containing nanocomposites were fabricated and showed improved photocatalytic activity, such as CQDs/metal oxide (CQDs/Fe₂O₃, CQDs/ZnO, and CQDs/SiO₂) [[27], [28], [29], [30]], CQDs/metal (CQDs/Au, CQDs/Cu) and ternary CQDs/metal/semiconductor (CQDs/Ag/Ag₃PO₄ and CQDs/Ag/Ag₃PW₁₂O₄₀) [[31], [32], [33]] composites. The CQDs in the nanocomposites promote the transfer of photoelectrons and hinder the recombination of charge carriers [[34], [35], [36]]. However, few studies discussed the effect of electron transfer direction and the relative contributions of UCPL and charge separation, which are critical for explaining the high photocatalytic activity.

Herein, we developed cost-effective spicule CQDs/FeOOH nanocomposite photocatalysts using a facile hydrothermal process and tested them for NO_X removal at ambient levels. Through comprehensive experimental characterization and density functional theory (DFT) calculations, we compared the photocatalytic behavior of the CQDs/FeOOH composites with that of pure FeOOH and discuss potential mechanisms.

Section snippets

Synthesis of CQDs/FeOOH nanocomposites

All reagents were of analytical grade and used without further purification. The CQDs/FeOOH nanocomposites were synthesized using a hydrothermal route by adding various amounts of CQDs to an iron precursor solution. Specifically, 12 mmol of Fe (NO₃)₃·9H₂O was dissolved in 20 mL of deionized water; then, 48 mmol of KOH solution was added dropwise under vigorous stirring. The dispersed suspension was sonicated for 30 min and different volumes of a CQDs solution were added. Subsequently, a mixture

Phase structure and surface elemental composition

The powder XRD patterns of the as-prepared C-Fe-2.5 nanocomposite and the pristine α-FeOOH samples are shown in Fig. 1a. Typical diffraction peaks were located at 2θ values of 21.2°, 33.2°, 36.6°, 41.3°, and 53.3° corresponding to the (110), (130), (111), (140), and (221) planes of orthorhombic goethite α-FeOOH with a unit cell of a = 4.608, b = 9.956, and c = 3.022 Å (JCPDS file No. 29–0713). No other impurity peaks were detected, suggesting that pure α-FeOOH was synthesized. The C-Fe-2.5

Conclusions

In summary, CQDs/FeOOH composites exhibited enhanced NO removal efficiencies compared to pure FeOOH under both solar and visible light. Experimental and theoretical investigations showed that fast separation and transfer of photo-excited carriers due to the addition of CQDs were the dominant factors for effective light utilization and enhanced photoactivity. Good biocompatibility and low cytotoxicity of the composite was demonstrated. In addition, carbon- and iron-containing catalysts use

Conflict of interest

Notes: The authors declare no competing financial interest.

Acknowledgements

This research was financially supported by the National Key Research and Development Program of China (grant No. 2016BBBMBYFA0203000), also partially supported by State Key Lab of Loess and Quaternary Geology (SKLLQGPY1605) and the National Science Foundation of China (Grant No. 41401567 and 41573138). Y.H. was supported by the “Hundred Talent Program” of the Chinese Academy of Sciences.

References (52)

J. Lasek et al.
Removal of NOx by photocatalytic processes
J. Photochem. Photobiol. C
(2013)
X. Qiu et al.
Degradation of decabromodiphenyl ether by nano zero-valent iron immobilized in mesoporous silica microspheres
J. Hazard. Mater.
(2011)
L.V.C. Lima et al.
Synergism between n-type WO₃ and p-type δ-FeOOH semiconductors: high interfacial contacts and enhanced photocatalysis
Appl. Catal. B Environ.
(2015)
S. Wang et al.
Controlling charge transfer in quantum-size titania for photocatalytic applications
Appl. Catal. B: Environ.
(2017)
A.C. da Silva et al.
Improved photocatalytic activity of δ-FeOOH by using H₂O₂ as an electron acceptor
J. Photochem. Photobiol. A: Chem.
(2017)
H.Y. Wu et al.
Solvothermal synthesis of green-fluorescent carbon nanoparticles and their application
J. Lumin.
(2012)
T.C. Araújo et al.
Hybrid heterostructures based on hematite and highly hydrophilic carbon dots with photocatalytic activity
Appl. Catal. B: Environ.
(2016)
H. AbdelSamad et al.
An XPS study of the adsorption of chromate on goethite (alpha-FeOOH)
Appl. Surf. Sci.
(1997)
H. Abdel-Samad et al.
An XPS study of the adsorption of lead on goethite (alpha-FeOOH)
Appl. Surf. Sci.
(1998)
Q. Zhang et al.
Perovskite LaFeO₃ -SrTiO₃ composite for synergistically enhanced NO removal under visible light excitation
Appl. Catal. B: Environ.
(2017)

Q. Tian et al.

Novel photocatalyst, Bi₂Sn₂O₇, for photooxidation of As (III) under visible-light irradiation

Appl. Catal. A: Gen.

(2012)

P. Granger et al.

Catalytic NOx abatement systems for mobile sources: from three-way to lean burn after-Treatment technologies

Chem. Rev.

(2011)

R.J. Huang et al.

High secondary aerosol contribution to particulate pollution during haze events in China

Nature

(2014)

W. Cui et al.

Highly efficient performance and conversion pathway of photocatalytic NO oxidation on SrO-Clusters@Amorphous carbon nitride

Environ. Sci. Technol.

(2017)

S. Liu et al.

Enhanced photocatalytic degradation of environmental pollutants under visible irradiation by a composite coating

Environ. Sci. Technol.

(2017)

H.B. Guo et al.

Naturally occurring iron oxide nanoparticles: morphology, surface chemistry and environmental stability

J. Mater. Chem. A

(2013)

J.L. Jambor et al.

Occurrence and constitution of natural and synthetic ferrihydrite, a widespread iron oxyhydroxide

Chem. Rev.

(1998)

Y. Zhang et al.

Nonmetal P-doped hematite photoanode with enhanced electron mobility and high water oxidation activity

Energy Environ. Sci.

(2015)

Y. Xu et al.

The absolute energy positions of conduction and valence bands of selected semiconducting minerals

Am. Mineral

(2000)

J. Liu et al.

Amorphous FeOOH quantum dots assembled mesoporous film anchored on graphene nanosheets with superior electrochemical performance for supercapacitors

Adv. Funct. Mater.

(2016)

W. Xu et al.

Interwoven heterostructural Co₃O₄–carbon@FeOOH hollow polyhedrons with improved electrochemical performance

J. Mater. Chem. A

(2016)

J.X. Feng et al.

FeOOH/ Co/FeOOH hybrid nanotube arrays as high-performance electrocatalysts for the oxygen evolution reaction

Angew. Chem.

(2016)

J.X. Feng et al.

Design and synthesis of FeOOH/CeO₂ heterolayered nanotube electrocatalysts for the oxygen evolution reaction

Adv. Mater.

(2016)

Z. Lian et al.

Pt-Enhanced mesoporous Ti³⁺/TiO₂ with Rapid bulk to surface electron transfer for photocatalytic hydrogen evolution

ACS Appl. Mater. Interfaces

(2017)

Z. Lian et al.

Plasmonic silver quantum dots coupled with hierarchical TiO₂ nanotube arrays photoelectrodes for efficient visible-light photoelectrocatalytic hydrogen evolution

Sci. Rep.

(2015)

H. Qi et al.

High pseudocapacitance in FeOOH/rGO composites with superior performance for High rate anode in Li-Ion Battery

ACS Appl. Mater. Interfaces

(2016)

Cited by (127)

Atomically dispersed Mn sites on TiO<inf>2</inf>(B) microspheres enables efficient photocatalytic abatement of NOx
2024, Separation and Purification Technology
While photocatalytic technology has been recognized as an effective means for removing low-concentration NOx in ambient atmosphere, it still faces the challenge of the deep oxidation in high efficiency. In many cases, the release of more toxic NO₂ byproduct appeared to be inevitable during the photocatalytic oxidation of NO. Herein we report that the atomically dispersed MnO_x cocatalyst on TiO₂(B) microspheres could significantly enhance the deep oxidation of NOx under mild photocatalytic conditions (1 mW/cm² UV-A light, 1 L/min flow rate). At an initial NO concentration of 0.35 ppm, ca. 67.15% of NO is oxidized on the MT-0.5 sample, which is 2.76 times higher than the pristine TiO₂(B) sample. More importantly, the release of NO₂ is suppressed by 2.11 times. Comprehensive spectral analyses suggest that atomically dispersed MnO_x effectively promotes the charge separation of photogenerated carriers in TiO₂(B), even better than MnO_x nanoparticles-loaded TiO₂(B). EPR and in-situ FTIR analyses illustrate that atomically dispersed MnO_x-loaded TiO₂(B) sample exhibits excellent low concentration NOx abatement performance, thus providing a rational mechanism for the NO deep oxidation pathway. This study not only provides a unique approach for preparing non-noble metal atomically dispersed co-catalysts, but also affords an effective means for efficient photocatalytic NO degradation.
Modulation of internal electric field engineering of bifunctional multi-interfacial heterojunction photocatalysts for photocatalytic H<inf>2</inf> and H<inf>2</inf>O<inf>2</inf> production
2024, Journal of Materiomics
The purposeful construction of dual Z-scheme system to the formation of intimate interface contact and multi-channel charge flow through the system remains a huge challenge. Herein, a tandem 2D/0D/2D g-C₃N₄ nanosheets/FeOOH quantum dots/ZnIn₂S₄ nanosheets (CNFeZn) dual Z-scheme system (DZSS) has been successfully constructed using electrostatic self-assembly method. Owing to the band structure and elaborate morphology of 2D g-C₃N₄, 0D FeOOH and 2D ZnIn₂S₄ in unique designed DZSS, plenty of spatial charge transfer channels are formed between the g-C₃N₄/FeOOH and FeOOH/ZnIn₂S₄ interfaces, which greatly accelerate the charge separation and transfer. As bifunctional catalysts, CNFeZn DZSS achieves the highest H₂ evolution rate of ∼436.6 μmol/h with a great promotion of ∼10.6 folds and ∼6.9 folds compared to pristine g-C₃N₄ and ZnIn₂S₄, respectively. Meanwhile, the H₂O₂ production rate reached ∼301.19 μmol/L after 60 min irradiation, up to ∼5.1 times and ∼2.3 times that of pristine g-C₃N₄ and ZnIn₂S₄. Experiment and DFT calculation further confirmed that the stable double built-in electronic field can be formed owing to the electron configuration between double interfaces, and reveal that the ample atomic-level charge transfer channels were established in the strong interaction connected double interfaces, which can act as the charge migration pathway promote the separation of photogenerated charges.
Efficient peroxymonosulfate activation and As(III) removal derived from Mn-FeOOH@nitrogen-deficient porous nanosheets: Key role of the N/O double vacancy
2024, Applied Surface Science
Nitrogen deficient porous nanosheets(NDCN) are a promising nano template that can combine defect engineering with Mn-FeOOH to suppress photo generated carrier complexation and optimize electron distribution. In this study, a unique structure with N/O double vacancies in Mn-FeOOH@NDCN was prepared using a magnesium thermal denitrification co-precipitation method. Furthermore, a series of Mn-FeOOH/NDCN/PMS reaction systems were constructed by adjusting the dosage of peroxymonosulfate(PMS). The experimental results indicate that the synergistic activation of N/O double vacancies on PMS enables the Mn-FeOOH/NDCN/PMS system to oxidize almost 10 mg/L of As(III) within 90 min. At the same time, the oxidized As(V) was completely adsorbed, thereby completely removing the total arsenic in the water. The reasonable construction of carbon networks is a prerequisite for the stability of Mn-FeOOH/NDCN composite catalysts, enabling them to have good cyclic stability. The experimental results confirm that oxygen vacancies directly participate in the activation of PMS, while nitrogen vacancies effectively adsorb As(III), thereby promoting the contact between As(III) and PMS, improving the mass transfer rate, and accelerating the catalytic degradation process. This study will provide a new way to completely remove arsenic pollution from water bodies.
Shape stability control of a 3D-printed clay/biochar-based monolith to support Fe catalyst for continuous levofloxacin degradation with low metal leaching
2024, Colloids and Surfaces A: Physicochemical and Engineering Aspects
Disposing of wet solid waste sludge has become a prominent issue because it has high environmental risks. Herein, a clay/biochar-based monolith (CBM) is prepared using a three-dimensional (3D) printing design method. The CBM is loaded with iron (Fe) and used as a catalyst (Fe/CBM) to activate peroxymonosulfate (PMS) for degrading levofloxacin (LVF) in an aqueous solution. The monolith preparation process is inexpensive, and the monolith has designable flow paths that facilitate improved mass transport and material recycling. ZnCl₂, as a chemical activator, is added to the 3D-printed slurry to improve the catalytic performance of Fe/CBM. Oscillatory stress sweep and frequency sweep tests prove that incorporating ZnCl₂-containing sludge in the slurry effectively increases the elastic modulus and critical stress, improving structural stability and constructability. The slurry containing 10% sludge (S_10%-Zn with 1 M ZnCl₂), exhibits 30% higher static yield stress than the slurry containing only clay and water (S_0%). Fe/CBM is prepared by loading Fe active sites onto the surface of CBM via an impregnation method, and it leaches very low amounts of Fe ( $<$ 0.2 mg/L) and other heavy metals (e.g., Cd, and Pd, etc). Fe/CBM-S_10%-Zn/PMS with 10% mass fraction of sludge exhibits much higher (∼80% at 20 min) degradation efficiency than Fe/CBM-S_0%/PMS (∼15% at 20 min) and Fe/CBM-S_10%/PMS (∼43% at 20 min). Combining with XPS results, when ZnCl₂ is added to the slurry, the content of Fe²⁺ in the catalytic material increases, improving the catalytic performance. The PMS activation mechanism of Fe/CBM-S_10%-Zn for LVF degradation is also discussed, which is ascribed to the radical and nonradical pathways. This provides new insights on how to recycle solid waste and make high-performance clay/biochar-based monolith catalysts for the continuous wastewater treatment.
Research progress in β-Fe<inf>2</inf>O<inf>3</inf>-based catalysts: An overview of the synthesis, conversion and applications
2023, Journal of Environmental Chemical Engineering
Fe₂O₃, as a substance that exists in nature in large quantities, has been widely paid close attention by many scholars because of its excellent properties. Fe₂O₃ can be divided into four phases depending on the crystal structure. As a narrow band gap semiconductor, β-Fe₂O₃ has a band gap of about 1.77–1.83 eV, which is much lower than the average band gap of Fe₂O₃ (2.1 eV), and its theoretical saturated photocurrent density is 35% higher than that of α-Fe₂O₃, showing excellent light absorption characteristics and water oxidation capacity, which is a promising photoanode material. As the only polycrystalline phase of iron oxide that exhibits paramagnetism at room temperature, it also has a very bright prospect in the field of magnetic resonance. This paper focuses on the review of rare phase β-Fe₂O₃. Firstly, the crystal structure, magnetism of β-Fe₂O₃ and the mature methods for preparing pure β-Fe₂O₃ are summarized. Secondly, the conversion relationships between β phase and other phases of Fe₂O₃ is reviewed, and the important factors affecting this process are summarized. As for the improvement and applications, it points out a variety of improvement methods such as heterojunction, element doping and morphology control, and discusses the applications of β-Fe₂O₃ in many fields such as photocatalysis, Fenton oxidation, photochemical hydrogen production, biomedicine and toxic gas detection. Finally, the application prospect and challenges of β-Fe₂O₃ are prospected. This paper aims to further demonstrate the latent capacity of β-Fe₂O₃. It also provides ideas for the application of this substance in other environmental remediation fields.
Graphitic carbon nitride (g–C<inf>3</inf>N<inf>4</inf>)–assisted materials for the detection and remediation of hazardous gases and VOCs
2023, Environmental Research
Graphitic carbon nitride (g–C₃N₄)–based materials are attracting attention for their unique properties, such as low-cost, chemical stability, facile synthesis, adjustable electronic structure, and optical properties. These facilitate the use of g-C₃N₄ to design better photocatalytic and sensing materials. Environmental pollution by hazardous gases and volatile organic compounds (VOCs) can be monitored and controlled using eco-friendly g–C₃N₄– photocatalysts. Firstly, this review introduces the structure, optical and electronic properties of C₃N₄ and C₃N₄ assisted materials, followed by various synthesis strategies. In continuation, binary and ternary nanocomposites of C₃N₄ with metal oxides, sulfides, noble metals, and graphene are elaborated. g-C₃N₄/metal oxide composites exhibited better charge separation that leads to enhancement in photocatalytic properties. g-C₃N₄/noble metal composites possess higher photocatalytic activities due to the surface plasmon effects of metals. Ternary composites by the presence of dual heterojunctions improve properties of g-C₃N₄ for enhanced photocatalytic application. In the later part, we have summarised the application of g-C₃N₄ and its assisted materials for sensing toxic gases and VOCs and decontaminating NOx and VOCs by photocatalysis. Composites of g-C₃N₄ with metal and metal oxide give comparatively better results. This review is expected to bring a new sketch for developing g–C₃N₄–based photocatalysts and sensors with practical applications.

View all citing articles on Scopus

View full text

Biocompatible FeOOH-Carbon quantum dots nanocomposites for gaseous NOx removal under visible light: Improved charge separation and High selectivity

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis of CQDs/FeOOH nanocomposites

Phase structure and surface elemental composition

Conclusions

Conflict of interest

Acknowledgements

J. Photochem. Photobiol. C

J. Hazard. Mater.

Appl. Catal. B Environ.

Appl. Catal. B: Environ.

J. Photochem. Photobiol. A: Chem.

J. Lumin.

Appl. Catal. B: Environ.

Appl. Surf. Sci.

Appl. Surf. Sci.

Appl. Catal. B: Environ.

Appl. Catal. A: Gen.

Catalytic NOx abatement systems for mobile sources: from three-way to lean burn after-Treatment technologies

Chem. Rev.

High secondary aerosol contribution to particulate pollution during haze events in China

Nature

Highly efficient performance and conversion pathway of photocatalytic NO oxidation on SrO-Clusters@Amorphous carbon nitride

Environ. Sci. Technol.

Enhanced photocatalytic degradation of environmental pollutants under visible irradiation by a composite coating

Environ. Sci. Technol.

Naturally occurring iron oxide nanoparticles: morphology, surface chemistry and environmental stability

J. Mater. Chem. A

Occurrence and constitution of natural and synthetic ferrihydrite, a widespread iron oxyhydroxide

Chem. Rev.

Nonmetal P-doped hematite photoanode with enhanced electron mobility and high water oxidation activity

Energy Environ. Sci.

The absolute energy positions of conduction and valence bands of selected semiconducting minerals

Am. Mineral

Amorphous FeOOH quantum dots assembled mesoporous film anchored on graphene nanosheets with superior electrochemical performance for supercapacitors

Adv. Funct. Mater.

Interwoven heterostructural Co3O4–carbon@FeOOH hollow polyhedrons with improved electrochemical performance

J. Mater. Chem. A

FeOOH/ Co/FeOOH hybrid nanotube arrays as high-performance electrocatalysts for the oxygen evolution reaction

Angew. Chem.

Design and synthesis of FeOOH/CeO2 heterolayered nanotube electrocatalysts for the oxygen evolution reaction

Adv. Mater.

Pt-Enhanced mesoporous Ti3+/TiO2 with Rapid bulk to surface electron transfer for photocatalytic hydrogen evolution

ACS Appl. Mater. Interfaces

Plasmonic silver quantum dots coupled with hierarchical TiO2 nanotube arrays photoelectrodes for efficient visible-light photoelectrocatalytic hydrogen evolution

Sci. Rep.

High pseudocapacitance in FeOOH/rGO composites with superior performance for High rate anode in Li-Ion Battery

ACS Appl. Mater. Interfaces

Biocompatible FeOOH-Carbon quantum dots nanocomposites for gaseous NO_x removal under visible light: Improved charge separation and High selectivity

Interwoven heterostructural Co₃O₄–carbon@FeOOH hollow polyhedrons with improved electrochemical performance

Design and synthesis of FeOOH/CeO₂ heterolayered nanotube electrocatalysts for the oxygen evolution reaction

Pt-Enhanced mesoporous Ti³⁺/TiO₂ with Rapid bulk to surface electron transfer for photocatalytic hydrogen evolution

Plasmonic silver quantum dots coupled with hierarchical TiO₂ nanotube arrays photoelectrodes for efficient visible-light photoelectrocatalytic hydrogen evolution