• • Dual-site 10%K–N%P@bamboo powder raised dry-basis char yield from 49.7% to 53.1% at 553 K for 15 min, a 3.4 percentage-point gain, while the air-dried high heating value of the char remained essentially unchanged; this directly improves solid carbon productivity without sacrificing fuel quality.
• • Single-site 15%K2CO3@bamboo powder reduced dry-basis char yield to 30.3% and raised char heating value to 26.67 MJ/kg, i.e., a 39% yield loss and 14.1% heating value gain versus raw bamboo powder; this confirms that alkali-only loading is unsuitable for carbonization processes targeting char as the primary product.
• • Ash content of bamboo char increased only from 0.86% to 0.96% with the dual-site material, a 0.10 percentage-point increment, indicating that the additive does not materially degrade char quality or combustion behavior.
• • The carbon-fixation mechanism is attributed to a three-dimensional network formed by P and K species on the bamboo surface that promotes secondary cracking of pyrolysis volatiles; this surface-confined architecture allows lower additive loadings than conventional solid additives, reducing separation and cost penalties.