Page 209 - AJWEP-22-4

Bombax ceiba-based carbons for dye removal

Bc-H demonstrated the highest removal efficiency Furthermore, π–π stacking between the aromatic rings
and fastest kinetics, achieving 99.9% removal within of RhB and graphitic domains in the carbon matrix
2 – 4 min. Commercial AC performed moderately likely contributes to the strong adsorption affinity. 31
well, reaching ~85 – 90% removal after ~10 min. In addition to its technical merits, Bc-H offers
In contrast, Bc-K and Bc-Na showed limited and significant economic advantages. The precursor, B. ceiba
negligible adsorption, respectively. These results sawdust, is a readily available, low-cost byproduct from
underscore the superior textural and surface chemical sawmills in Nepal. The one-step H PO activation at
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3
properties of Bc-H, which arise from its high BET moderate temperature (400°C) minimizes chemical and
surface area, phosphate-linked oxygenated groups, energy consumption. These factors highlight Bc-H’s
and balanced micro/mesoporous structure. 28,29 These potential for cost-effective and scalable application,
features distinguish Bc-H not only from the other especially in resource-limited regions.
synthesized samples but also from the commercial We acknowledge that all samples were carbonized
benchmark. at a fixed temperature of 400°C to isolate the effect of
Although FTIR spectroscopy was used to identify activating agents. However, KOH and Na CO may
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2
key surface functionalities before dye exposure, post- benefit from higher activation temperatures, and future
adsorption spectroscopic analyses (e.g., FTIR, X-ray work will explore this variable to optimize textural and
photoelectron spectroscopy) were not performed. adsorptive properties.
Therefore, the proposed adsorption mechanism – based
on electrostatic attraction, hydrogen bonding, and π–π 3.3.5. Comparison with literature
interactions – is supported indirectly by structural and To further contextualize the performance of Bc-H,
kinetic data. This limitation has been noted, and future Table 5 presents a comparison with RhB adsorption
studies will include point of zero charge measurements data reported for various biomass-derived adsorbents.
and post-adsorption spectral analysis to provide direct While most of the listed adsorbents achieved removal
evidence of adsorbent–adsorbate interactions. 30 efficiencies above 90%, they generally required higher
The high surface area and well-developed dosages (0.04 – 0.05 g/100 mL) and longer contact times
mesoporous structure of Bc-H facilitate rapid dye (30 – 120 min). In contrast, Bc-H removed 99.9% of RhB
diffusion, while oxygenated surface groups enhance in just 2 – 4 min at a lower dose (0.03 g), underscoring
electrostatic and hydrogen bonding interactions. its outstanding kinetics and practical efficiency.

Table 4. Comparative rhodamine B adsorption performance of carbons under identical conditions
Adsorbent Brunauer–Emmett– Rhodamine B Time for~99.9% pH Dose
teller surface area (m /g) removal (%) removal (g/100 mL)
2
Bc-H 1,451.2 99.9 2 – 4 min 8.5 0.03
Bc-K 78.4 ~45 >10 min 8.5 0.03
Bc-Na 61.2 Negligible - 8.5 0.03
CAC 989.3 96.4 ~6 min 8.5 0.03
Note: Bc-H, Bc-K, and Bc-Na refer to acid-activated, base-activated, and salt-activated carbons, respectively.
Abbreviation: CAC: Commercial activated carbon.

Table 5. Comparison of rhodamine B removal performance between phosphoric acid-activated carbon
and other reported biomass-based adsorbents
Adsorbent (Precursor) Rhodamine B removal (%) Contact time Dose (g/100 mL) Reference
Phosphoric acid-AC (this study) 99.9 2–4 min 0.03 This work
Rice husk biochar 92 60 min 0.05 10
Moringa seed pod AC 94 90 min 0.04 28
Casuarina cone powder 89 120 min 0.05 29
Elaeagnus stone AC 93 30 min 0.05 30
Abbreviation: AC: Activated carbon.

Volume 22 Issue 4 (2025) 201 doi: 10.36922/AJWEP025240191