A study reports 98% and 97% yields for two model chemical reactions using an amine-functionalized biochar made from walnut shells. Both reactions were run in water at room temperature, and the material was recovered and reused for five successive cycles without a significant decrease in catalytic activity or product yield.
For the naphthyridine reaction, the optimization table reports a 98% yield in 20 minutes with 0.04 grams of catalyst in water at 25 °C. Listed comparison rows using biochar, nitrated biochar and no catalyst gave yields of 35%, 43% and 35%, respectively, after 120 minutes.
For the chromene reaction, the optimization table reports a 97% yield in seven minutes under the reported model setup, with 0.04 grams of catalyst in 5 millilitres of water at 25 °C. The listed comparison rows gave 48%, 52% and 48%, respectively, after 120 minutes. The paper contains an internal discrepancy because another comparison table gives a different reaction time for this result.
Turning shell waste into a catalyst
The starting biochar was prepared from walnut shells by pyrolysis and then modified through nitration and reduction to produce biochar-NH2. The paper used the modified material as a heterogeneous nanocatalyst, a catalyst that could be recovered from the reaction mixture for reuse.
The reported model naphthyridine reaction used 1 millimole each of 2,6-diaminopyridine, an aromatic aldehyde and malononitrile, with 0.04 grams of catalyst in 5 millilitres of water at room temperature. The chromene model used 1 millimole each of resorcinol, malononitrile and an aromatic aldehyde, again with 0.04 grams of catalyst in 5 millilitres of water at room temperature.
The researchers characterized the material using scanning electron microscopy, surface-area measurements, infrared spectroscopy, elemental analysis and X-ray diffraction. They reported changes in functional groups and morphology after modification, along with an increase in specific surface area. BET analysis gave an average pore diameter of 13.0 nanometres, a specific surface area of 3.2 square metres per gram and a pore volume of 0.011 cubic centimetres per gram.
Results varied with the starting chemicals
Beyond the model run, the team tested different aromatic aldehydes in the naphthyridine reaction. The authors reported good to outstanding results across the examples and said aldehydes carrying electron-withdrawing groups were more reactive than those carrying electron-donating groups.
A similar pattern was reported for the chromene reaction. Various aldehydes gave good to excellent results in water at room temperature, with electron-withdrawing aldehydes described as more reactive than electron-donating aldehydes. Complete numerical results for every substrate were not provided in the supplied analysis, so the scope cannot be reduced to one overall yield.
The comparisons show how the modified material performed against the listed controls in these tests. They do not establish that amine functionalization alone caused the yield differences or that the catalyst would outperform every conventional system under matched conditions.
The reusability test reported recovery and reuse across five successive cycles without any significant decrease in catalytic activity or product yield. The study did not provide cycle-specific yields or a quantified activity-retention curve, so the durability result remains a qualitative five-cycle finding.
Promising chemistry, limited evidence
The authors say the study was limited to a few reactions and starting materials. They suggest testing more starting materials at larger scale to assess the catalyst’s performance and possible industrial applications, making scale-up a proposed next step rather than a demonstrated result.
The model yields and reaction times were reported without replicate counts or variability estimates. That leaves uncertainty about how consistently the same results would be obtained across repeated runs.
The study therefore supports a laboratory demonstration of a renewable, water-compatible catalyst in the tested reactions. It does not establish general performance across all aldehydes or reaction classes, or readiness for larger-scale production.
The authors acknowledge financial support from Bu-Ali Sina University and declare no competing financial interests. They state that the datasets are available from the corresponding author upon reasonable request and that generated or analyzed data are included in the article and supplementary information.
Paper data and sources
Original title: Amine-functionalized biochar as a green and recyclable nanocatalyst for the efficient synthesis of 1,8-naphthyridine and 2-amino-4-chromene derivatives.
Authors: Reza Hazbavi, Maryam Hajjami, Mohammad Ali Zolfigol, Zahra Siahpour
Journal/Repository: RSC advances
Status: Peer-reviewed
First online: 2026-08-20
DOI: 10.1039/d6ra05766g
Original paper