Key Takeaways & Executive Findings
- •• • Fe2.5/Ni5–ACF achieved 99.88% conversion of 4-NP within 10 min using 0.26 mol L−1 NaBH4, outperforming several reported catalysts (e.g., AgNi/PC@Mn NPs: >99% in 16 min; Ni/Co/Cu–ACF: 98.5% in 10 min) and demonstrating superior kinetics for wastewater treatment. • • The coal tar pitch-based ACF support exhibited a specific surface area of 1847 m2/g with micropores accounting for 97.6% of total pore volume, providing abundant active sites for metal nanoparticle dispersion and enhancing catalytic activity through adsorption synergy. • • Optimal synthesis conditions were identified: reaction temperature 45 °C, 4-NP concentration 2.5 mmol L−1, and Fe3+:Ni2+ molar ratio of 1:2 (total 7.5 mmol L−1), yielding a catalyst with an average nanoparticle diameter of ~100 nm and stable recyclability over five cycles. • • The hydrothermal–calcination method enables cost-effective loading of non-precious bimetallic Fe–Ni nanoparticles onto ACFs, offering a scalable alternative to precious metal catalysts for industrial 4-NP reduction, with potential for treating high-strength wastewater.
Abstract
The reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in wastewater faces challenges in conversion rate and stability. We used coal tar pitch-based activated carbon fibers (ACFs) as a support material for loading transition metal catalysts to catalyze the reaction. Fe–Ni nanoparticles were loaded onto the coal tar pitch-based ACF through a simple hydrothermal–calcination method. The results showed that the coal tar pitch-based ACFs had a high specific surface area (1847 m2/g) and a unique microporous structure, and the metals were loaded onto them. The average diameter of the nanoparticles formed was approximately 100 nm. By changing the metal loading it was shown that the performance was best when the reaction temperature was 45 °C, the 4-NP concentration was 2.5 mmol L−1, and the molar concentration ratio of Fe3+ to Ni2+ was 1∶2 (total 7.5 mmol L−1). Under these conditions the conversion efficiency reached 99.88%. Fe2.5/Ni5–ACF exhibited excellent catalytic activity and recyclability for 4-NP after five cycles. The inherent advantages of nanomaterials increase the catalytic efficiency of 4-NP, which expands the use of coal tar pitch-based ACFs as supporting materials in the field of catalysis.
1. Introduction
The catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using NaBH4 is a benchmark reaction for wastewater treatment, yet commercial adoption is hindered by the high cost and scarcity of precious metal catalysts (e.g., Pd, Au, Ag) and the poor stability of non-precious metal nanoparticles. Conventional supports like metal oxides often suffer from low surface area and weak metal-support interactions, leading to agglomeration and rapid deactivation. Coal tar pitch-based activated carbon fibers (ACFs) offer a compelling alternative due to their ultra-high specific surface area (1847 m2/g) and microporous structure (97.6% micropore volume), which can stabilize nanoparticles and enhance mass transfer. However, previous attempts to load bimetallic catalysts on carbon supports have not fully exploited the synergistic effects of Fe and Ni, nor have they systematically optimized metal ratios and reaction conditions.
This study addresses these bottlenecks by employing a simple hydrothermal–calcination method to load Fe–Ni nanoparticles onto coal tar pitch-based ACFs. The resulting Fe2.5/Ni5–ACF catalyst achieves 99.88% conversion of 4-NP within 10 minutes under optimized conditions (45 °C, 2.5 mmol L−1 4-NP, Fe3+:Ni2+ = 1:2), outperforming many reported catalysts. The high surface area and microporosity of the ACF support, combined with the uniform dispersion of ~100 nm bimetallic nanoparticles, enable a synergistic adsorption-catalysis mechanism that ensures high activity and recyclability over five cycles. This work demonstrates a cost-effective, scalable route to efficient 4-NP reduction, expanding the application of coal tar pitch-based ACFs in environmental catalysis.
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Li Fuhu, You Jing, Zhang Qianyu, Zhang Ye, Rong Junfeng (2026). Loading of Nano-Bimetallic Catalysts onto Coal Tar Pitch-Based Activated Carbon Fibers for Efficient Reduction of p-Nitrophenol. New Carbon Materials. https://doi.org/10.1016/S1872-5805(26)61067-0
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Frequently Asked Questions
What is the long-term stability of Fe2.5/Ni5–ACF under continuous flow conditions, and what are the primary deactivation mechanisms?
The study reports recyclability over five cycles with no significant loss in activity, but long-term stability under continuous flow is not addressed. Potential deactivation mechanisms include nanoparticle agglomeration, leaching of Fe/Ni ions, and fouling by reaction byproducts. The high surface area and microporous structure of the ACF support may mitigate agglomeration, but further studies are needed to assess metal leaching and structural integrity over extended operation.
How does the catalytic performance of Fe2.5/Ni5–ACF compare to precious metal catalysts on a cost-normalized basis, and what is the estimated cost per kilogram of 4-NP converted?
The paper does not provide a cost analysis, but Fe and Ni are significantly cheaper than precious metals like Pd or Au. The catalyst achieves 99.88% conversion in 10 minutes, comparable to or better than many precious metal systems (e.g., Pd1-(SnOx)0.75@pSiO2: >99% in 15 min). A rough estimate suggests that the material cost of Fe2.5/Ni5–ACF is orders of magnitude lower, making it economically attractive for large-scale wastewater treatment.
What is the optimal metal loading range, and how does exceeding the optimal Fe:Ni ratio affect catalytic activity and selectivity?
The optimal Fe3+:Ni2+ molar ratio was 1:2 (total 7.5 mmol L−1). The paper indicates that varying the metal loading affects performance, but it does not provide detailed data on off-optimal ratios. It is likely that excessive Ni or Fe leads to larger nanoparticles or altered surface chemistry, reducing active sites and catalytic efficiency. Further systematic studies are required to map the full composition-activity landscape.
How does the presence of micropores (97.6% of total pore volume) influence mass transfer of 4-NP and NaBH4 to the active sites, and could this limit reaction rates at higher concentrations?
The microporous structure provides a high surface area for metal dispersion and enhances adsorption of 4-NP, but micropores may impose diffusion limitations for larger molecules. At the tested concentration (2.5 mmol L−1), the reaction reaches 99.88% conversion in 10 minutes, indicating adequate mass transfer. However, at higher concentrations, pore diffusion could become rate-limiting. The study does not investigate this, but the high surface area and uniform nanoparticle distribution likely mitigate such effects.
What is the environmental footprint of the hydrothermal–calcination synthesis method, particularly regarding energy consumption and waste generation?
The paper does not provide a life-cycle assessment. Hydrothermal–calcination typically requires moderate temperatures (likely 150–200°C for hydrothermal and 300–500°C for calcination) and produces minimal liquid waste if metal salts are fully consumed. The use of coal tar pitch-based ACFs, derived from industrial byproducts, adds sustainability. However, a detailed environmental impact analysis is necessary to confirm the green credentials claimed.
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