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2026-08-06

Journal of Environ. Chem. Eng.: Latest research results of Zhang Liuxue's research group at Zhongyuan University of Technology in the field of photocatalytic phenyl hydroxylation.

Turning Coffee Waste into a Green Catalyst: Eu-Modified Fe-MOF/Biochar Composite for Photocatalytic Benzene Hydroxylation

Eu-modified Fe-MOF/biochar composite for photocatalytic benzene hydroxylation
First author
Jiaqi Zhang
Corresponding authors
Xu Jia, Xiulian Wang, and Liuxue Zhang

Research Highlights

  • Biochar derived from spent coffee grounds provides a sustainable support and enables value-added waste utilization.
  • Eu-ion doping tunes the electronic structure and creates synergistic Fe–Eu bimetallic active sites.
  • Coupling Fe–Eu MOFs with biochar effectively suppresses the recombination of photogenerated charge carriers.
  • The synergy between photocatalysis and Fenton-like reactions substantially enhances phenol yield and selectivity.

Introduction

In March 2026, the Journal of Environmental Chemical Engineering published online the latest work from Professor Liuxue Zhang’s team at Zhongyuan University of Technology in the field of photocatalytic benzene hydroxylation. The study reports a Eu-doped Fe-MOF/biochar composite photocatalyst prepared using biochar derived from spent coffee grounds, enabling the efficient, highly selective, and greener conversion of benzene to phenol. Jiaqi Zhang is the first author, while Xu Jia, Xiulian Wang, and Liuxue Zhang are the co-corresponding authors.

Overview of the Eu-doped Fe-MOF/biochar photocatalyst for converting benzene to phenol

Background

Conventional phenol production relies primarily on the multistep cumene process, which is associated with high energy consumption, substantial waste generation, and limited phenol selectivity. Solar-driven photocatalysis can operate under mild conditions and therefore offers an attractive route to greener phenol synthesis. Existing photocatalysts, however, are often constrained by rapid charge-carrier recombination and an insufficient number of active sites. Metal–organic frameworks (MOFs) offer high specific surface areas and tunable structures, but the catalytic efficiency of a single MOF phase remains limited.

In this study, Eu was incorporated into an Fe-based MOF, which was then integrated with biochar derived from spent coffee grounds. The high electrical conductivity and porous structure of the biochar accelerate electron transport and expose more accessible reaction sites. Meanwhile, the Fe3+/Fe2+ and Eu3+/Eu2+ redox cycles enhance the Fenton-like process and promote the formation of hydroxyl radicals (•OH), thereby enabling efficient photocatalytic hydroxylation of benzene to phenol.

Instrumentation Used in the Study

Perfectlight PCX-50C Discover Multi-Channel Photochemical Reaction System

PCX-50C Discover Multi-Channel Photochemical Reaction System

The system supports parallel catalyst screening, reaction-condition optimization, and substrate-scope evaluation in photochemical methodology research. Its nine-position LED irradiation platform improves experimental throughput while maintaining reliable comparability among parallel reactions. Selectable and customizable LED wavelengths span the ultraviolet to near-infrared regions, accommodating a broad range of photochemical synthesis applications.

Figure-by-Figure Analysis

SEM images of CF biochar, Fe-Eu-MOFs, and the Fe-Eu-MOFs/CF composite
Figure 1. SEM images of the catalysts. Key findings: CF biochar exhibits a loose, porous structure (a); Fe–Eu MOFs display a well-defined octahedral morphology (b); and the octahedral particles are uniformly anchored on the biochar surface in the Fe–Eu-MOFs/CF composite (c), confirming successful composite formation.
XRD patterns and FTIR spectra of the catalyst samples
Figure 2. XRD patterns and FTIR spectra. Key findings: The XRD patterns of the composite contain characteristic reflections associated with Fe-MOF, Eu-MOF, and graphitic carbon. In the FTIR spectra, the bands at 1,625 and 1,380 cm−1 are assigned to coordinated carboxylate groups, while those at 613, 541, and 452 cm−1 are attributable to Fe–O and Eu–O vibrations. These results confirm the successful synthesis and integration of the MOF and biochar components.
Effects of catalyst composition and dosage on phenol yield
Figure 3. Effects of catalyst composition and dosage on phenol yield. Key findings: (a) Fe–Eu-MOFs/CF-10% affords the highest phenol yield and clearly outperforms the pristine MOF and biochar controls. (b) The optimal catalyst dosage is 20 mg; higher loadings reduce the yield because of light-shielding effects.
Effects of hydrogen peroxide and trifluoroacetic acid dosages on phenol yield
Figure 4. Effects of H2O2 and trifluoroacetic acid dosages on phenol yield. Key findings: (a) The optimal H2O2 dosage is 2 mL; an excessive amount promotes overoxidation of phenol. (b) The optimal trifluoroacetic acid dosage is 0.1 g. A moderately acidic environment lowers the reaction activation barrier, whereas excess acid suppresses phenol formation.
Effects of reaction time and temperature on phenol yield
Figure 5. Effects of reaction time and temperature on phenol yield. Key findings: (a) The optimal reaction time is 5 h; prolonged irradiation favors the formation of by-products. (b) The optimal reaction temperature is 50 °C; higher temperatures accelerate H2O2 decomposition and may reduce catalyst activity.
Recycling stability and structural characterization of the catalyst
Figure 6. Recycling stability tests. Key findings: After five consecutive cycles, the phenol yield decreases only slightly and remains at a relatively high level. No pronounced changes are observed in the XRD patterns or FTIR spectra before and after reaction, demonstrating good catalyst stability and recyclability.
Reactive-species trapping experiments for photocatalytic benzene hydroxylation
Figure 7. Reactive-species trapping experiments. Key findings: The phenol yield decreases markedly after the addition of EDTA-2Na, a hole scavenger, or potassium dichromate, an electron scavenger. This result indicates that both photogenerated holes (h+) and electrons (e−) play essential roles in the reaction.
Proposed mechanism for photocatalytic hydroxylation of benzene over Fe-Eu-MOFs/CF
Scheme 1. Proposed photocatalytic reaction mechanism. Key findings: Under light irradiation, electrons are promoted to the conduction band, leaving holes in the valence band. The photogenerated electrons reduce O2 to superoxide radicals (•O2−), which are subsequently converted into H2O2. The Fe3+/Fe2+ and Eu3+/Eu2+ redox cycles promote Fenton-like reactions and generate •OH radicals that attack the benzene ring to form phenol. Biochar accelerates electron transport, while the bimetallic synergy suppresses charge-carrier recombination.

Summary

This study successfully constructed an Fe–Eu-MOFs/CF photocatalyst through the in situ growth of Fe–Eu MOFs on biochar derived from spent coffee grounds. Under the optimal reaction conditions—20 mg of catalyst, 2 mL of H2O2, 0.1 g of trifluoroacetic acid, and a reaction temperature of 50 °C for 5 h—the phenol yield reached 34.27%, with a selectivity of 96.26%. The catalyst also retained good activity after five cycles. This work offers a new route for the value-added utilization of spent coffee grounds and provides useful design principles for efficient and sustainable catalytic systems for phenol synthesis.

Author Profile

Liuxue Zhang is a professor at Zhongyuan University of Technology. His research focuses on the design of high-performance hybrid materials and their applications in photocatalysis. He has published more than 40 papers in peer-reviewed journals, including International Journal of Hydrogen Energy, Journal of Catalysis, and Journal of Environmental Chemical Engineering.

Publication Details

Jiaqi Zhang, Xu Jia, Xiulian Wang, Zhiqi Song, Lidan Yang, Liuxue Zhang, Jiaolong Qiao, and Yonggang Liu. “Turning coffee waste into a green catalyst: Eu-modified Fe-MOF/biochar composite for photocatalytic benzene hydroxylation.” Journal of Environmental Chemical Engineering 14 (2026): 122049. https://doi.org/10.1016/j.jece.2026.122049

Publication information for the Journal of Environmental Chemical Engineering article

Founded in 2006, Beijing Perfectlight Technology Co., Ltd. (Perfectlight) is recognized as a National High-Tech Enterprise, a Zhongguancun High-Tech Enterprise, and one of Beijing’s first Specialized, Refined, Distinctive, and Innovative enterprises. The company is certified to ISO 9001, ISO 14001, and ISO 45001, and its after-sales service has achieved a five-star rating under GB/T 27922-2011. Perfectlight specializes in the research, development, manufacturing, sales, and service of intelligent, high-precision, high-performance instruments and integrated solutions. Its portfolio covers more than ten product families, including irradiation light sources; photocatalytic, photoelectrocatalytic, photothermal, and thermal catalytic systems; characterization and testing platforms; research and pilot-scale equipment; and photochemical synthesis systems. These solutions support the entire workflow from fundamental research and laboratory or pilot studies to industrial scale-up. Serving universities, research institutes, and industrial customers in new energy, pharmaceutical synthesis, fine chemicals, and advanced materials, Perfectlight products are used in more than 3,000 laboratories across nearly 50 countries and have supported over 9,000 SCI-indexed publications. The company has led or participated in the development of national and industry standards, undertaken projects under China’s National Key R&D Program, secured multiple core intellectual-property rights and Beijing New Technology and New Product certifications, and helped industrial customers establish tonne-scale and 100-tonne-scale photochemical production lines.

Instrument featured in this article: The PCX-50C Discover Multi-Channel Photochemical Reaction System supports parallel catalyst screening, reaction-condition optimization, and substrate-scope evaluation in photochemical methodology research. The system features nine LED irradiation positions with customizable wavelengths spanning the ultraviolet to near-infrared regions, improving screening efficiency while preserving the comparability and reliability of parallel results.

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