Preparation of nitrogen-doped rice straw biochar activated by sodium bicarbonate and its adsorption of cadmium

doi:10.3969/j.issn.1004-1524.20250062

Acta Agriculturae Zhejiangensis ›› 2026, Vol. 38 ›› Issue (5): 944-954.DOI: 10.3969/j.issn.1004-1524.20250062

• Environmental Science • Previous Articles Next Articles

Preparation of nitrogen-doped rice straw biochar activated by sodium bicarbonate and its adsorption of cadmium

CHENG Kai¹^,²(), LI Feiyue¹, HE Lili²^,³, YANG Chenghu², WANG Yuying²^,³, LYU Haohao²^,³, YANG Shengmao²^,³, LIU Yuxue¹^,²^,³^,^*()

¹ College of Resource and Environment, Anhui Science and Technology University, Fengyang 233100, Anhui, China
² State Key Laboratory for Quality and Safety of Agro-Products, Institute of Soil, Fertilizer and Environmental Resources, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China
³ Engineering Research Center of Biochar of Zhejiang Province, Hangzhou 310021, China

Received:2025-01-18 Online:2026-05-25 Published:2026-06-02

Abstract

Abstract:

Nitrogen-doped rice straw biochar activated by sodium bicarbonate was prepared using rice straw as the biomass precursor, with urea and sodium bicarbonate serving as the nitrogen source and chemical activator, respectively. A series of adsorption experiments were conducted to investigate the cadmium ions (Cd²⁺) adsorption in aqueous solutions using the prepared rice straw biochar. The effects of various factors, including solution pH value, biochar addition amount, initial Cd²⁺ mass concentration in solution, temperature, ionic strength and coexisting ions, on the adsorption performance were systematically examined. Additionally, the adsorption mechanism was explored from the kinetic perspective. The results demonstrated that the combined effect of urea doping and sodium bicarbonate activation enhanced Cd²⁺ adsorption. Compared with the conventional rice straw biochar (BC), the biochar prepared with a mixing ratio of 2∶1∶1 for rice straw powder, sodium bicarbonate and urea (marked as BC2-1-1) exhibited a maximum Cd²⁺ adsorption capacity of 45.322 6 mg·g^-1, which was 5.27 times as that of BC. The adsorption of Cd²⁺ by biochar fitted well with the Langmuir isothermal adsorption model, and followed the pseudo-second-order kinetic equation, indicating a monolayer adsorption mechanism dominated by chemical adsorption. This study provided theoretical basis and technical support for the high-value utilization of rice straw and the remediation of cadmium-contaminated water.

Key words: rice straw biochar, nitrogen doping, chemical activation, cadmium, adsorption

CLC Number:

TQ424
X52

CHENG Kai, LI Feiyue, HE Lili, YANG Chenghu, WANG Yuying, LYU Haohao, YANG Shengmao, LIU Yuxue. Preparation of nitrogen-doped rice straw biochar activated by sodium bicarbonate and its adsorption of cadmium[J]. Acta Agriculturae Zhejiangensis, 2026, 38(5): 944-954.

Figures/Tables 9

Table 1 Physicochemical properties of the prepared biochar

样品 Sample	pH值 pH value	EC/ (μS·cm^-1)	w_C/%	w_N/%	w_H/%	w_O/%	H/C	O/C	SSA/ (m²·g^-1)	PV/ (cm³·g^-1)	APS/nm
BC	7.93±0.03	75.10±1.08	48.06	0.93	2.52	48.49	0.63	0.76	181.92	0.12	2.69
BC2-1-1	9.90±0.01	115.23±2.20	30.00	2.03	1.86	66.11	0.74	1.65	288.79	0.24	3.28
BC1-1-1	9.54±0.01	148.70±1.31	23.46	2.39	1.81	72.34	0.93	2.31	384.19	0.32	3.38

Fig.1 Infrared spectrum of prepared biochar BC, Prepared rice straw biochar. BC2-1-1 and BC1-1-1 represent the biochar made from rice straw, sodium and urea at the ratio of 2∶1∶1 and 1∶1∶1, respectively. The same as below.

Fig.2 X-ray photoelectron spectroscopy (XPS) of biochar a,BC;b,BC2-1-1;c,BC1-1-1。

Fig.3 Effects of pH value (a), initial mass concentration (b), biochar addition amount (c), and temperature (d) on the Cd2+ removal rate of biochar Bars marked without the same letters indicate significant (p<0.05) difference within varying temperature for the same biochar.

Fig.4 Adsorption kinetics models of Cd2+in solution by BC(a), BC2-1-1 (b), and BC1-1-1 (c) qe is the adsorption capacity at equilibrium; qt is the adsorption capacity at time t. The same as below.

Table 2 Parameters of pseudo-first-order and pseudo-second-order dynamics equations

样品 Sample	准一级动力学模型Pseudo-first-order model			准二级动力学模型Pseudo-second-order model
样品 Sample	q_e/(mg·g^-1)	R²	k₁/min^-1	q_e/(mg·g^-1)	R²	k₂/(g·mg^-1·min^-1)
BC	0.496 3	0.861 8	0.996 0	0.702 9	0.995 0	0.301 8
BC2-1-1	7.155 6	0.882 9	0.157 6	7.369 2	0.997 1	0.023 1
BC1-1-1	8.463 8	0.817 8	0.180 8	8.410 4	0.997 1	0.014 7

Fig.5 Isothermal adsorption models of Cd2+ in solution by BC (a), BC2-1-1 (b), and BC1-1-1 (c) Ce is the Cd2+ concentration in the solution at equilibrium, mg·L-1.

Table 3 Fitting parameters of isothermal adsorption models

样品 Sample	朗缪尔等温吸附模型 Langmuir isothermal adsorption model			弗罗因德利希等温吸附模型 Freundlich isothermal adsorption model
样品 Sample	q_m/(mg·g^-1)	k_L/(L·mg^-1)	R²	k_F/[mg·g^-1·(mg·L^-1)^-1/ⁿ)	1/n	R²
BC	8.605 8	0.996 6	0.997 2	4.771 7	0.173 4	0.856 4
BC2-1-1	45.322 6	0.222 3	0.990 9	9.068 4	0.850 1	0.932 1
BC1-1-1	40.322 6	0.307 7	0.991 5	9.583 1	1.096 9	0.878 9

Fig.6 Effects of solution ion strength (a),coexisting ions (b), and cycle times (c) on Cd2+ adsorption by BC2-1-1 Bars marked without the same letters indicate significant difference at p<0.05. None indicates control without coexisting ions introduced in the solution.

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Preparation of nitrogen-doped rice straw biochar activated by sodium bicarbonate and its adsorption of cadmium

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