Introduction

Phosphorus and nitrogen are essential elements for the growth of organisms, and the contents of phosphorus and nitrogen in the water are the important indicators of surface water and wastewater quality (Shao et al. 2022; Wu et al. 2020). However, the presence of high concentration of phosphorus and nitrogen will reproduce the excessive algae and the eutrophication in water body, which result in the deaths of many aquatic organisms (Huang et al. 2017; Lasfar et al. 2007). At present, the methods for removing nitrogen and phosphorus mainly include coagulation technology, biological method, chemical precipitation method, ion exchange method, membrane separation method, adsorption method, etc. (Arnaldos and Pagilla 2010; Cheng et al. 2021; Guida et al. 2021; Peng et al. 2021; Qiu et al. 2020). Among them, the adsorption method has the advantages of convenient operation, low cost, and high efficiency, which is a research hotspot in the treatment of nitrogen and phosphorus wastewater (Wang et al. 2020).

Biochar is considered as a high-quality adsorption material widely used in water purification with the merit of high carbon content, developed porosity, and surface area (Liu et al. 2021; Rodríguez Alberto et al. 2021). Many studies have indicated that the biochar had certain adsorption effect for phosphorus and nitrogen in aqueous solution (Li et al. 2021a; Yang et al. 2021c). Biochar could be prepared by a wide range of raw materials, such as activated sludge, straw, and cellulose (Lawal et al. 2021; Wang et al. 2021c; Zhang et al. 2020). The physical and chemical properties of biochar are affected by many factors such as raw materials, carbonization temperature, and surface modification (Chin et al. 2021; Kasera et al. 2021; Oginni and Singh 2021). At present, the effect of raw materials and carbonization temperature for control of physical and chemical properties of prepared biochar has been extensively investigated (Cao et al. 2019; Li et al. 2021b; Yang et al. 2021b).

The wetland plants release a large amount of nitrogen and phosphorus organic substances after they are decomposed, which easily causes the siltation and blockage of the wetland substrate and affects the growth of plants (Guo et al. 2021; Yu et al. 2020). Therefore, the decomposing of wetland plants has a significant impact on the operation effect and operation life of the constructed wetland (Trevathan-Tackett et al. 2021). Plant harvesting has a significant positive impact on the reduction of nitrogen and phosphorus in water bodies. The collected plants can be made into biochar for resource utilization (Tao et al. 2019). Thalia dealbata Fraser is a wetland perennial emergent plant, which has a fast growth and reproduction speed (Zhang et al. 2011). Therefore, Thalia dealbata Fraser is an ideal material for preparation of biochar and purifying wastewater (Cui et al. 2016a). Tao et al. prepared MgCl2-modified Thalia dealbata Fraser biochar (carbonization temperature at 500 °C) for ex situ remediation of Cd2+ and sulfonamide-contaminated lake sediments (Tao et al. 2019). Chu et al. studied the adsorption behavior and mechanism of anthraquinone dyes on phosphoric acid–activated Thalia dealbata Fraser biochar (carbonization temperature at 600 °C), with a maximum adsorption capacity of 555 mg/g (Chu et al. 2014). However, these studies mainly focus on the activation of biochar precursors and the surface modification of biochar. There are relatively few studies on the effect of carbonization temperature on biochar, which also play an important role in physical and chemical properties of biochar.

In this research, Thalia dealbata Fraser was used as carbon source for preparation of biochar. The chemical and physical properties of biochar prepared under different carbonization temperature were characterized using XRD, FTIR, SEM, and BET. The kinetic and isotherm behaviors of the ammonia nitrogen, nitrate, and phosphate adsorption process of biochar were investigated. The effect of pH on ammonia nitrogen, nitrate, and phosphate adsorption was studied. This paper realized the resource utilization of perennial emergent wetland plants and provided novel materials and approaches for environmental remediation.

Experimental

Materials and instruments

Preparation of Thalia dealbata Fraser–derived biochar

Thalia dealbata Fraser was collected from Wuhan Optics Valley Wetland Park in autumn. The stalk of Thalia dealbata Fraser was cleaned, air-dried naturally (7 days), and cut into piece. The obtained stalk piece was grinded and sieved through a 100-mesh sieve, which was used as the biomass precursor for biochar preparation. Ten grams of biomass precursor was put into the crucible, and then, the crucible was put into the vacuum resistance furnace to carbonize the biomass. The parameter for carbonization was set as follows: nitrogen flow rate at 0.5 l/min, heating rate at 8 °C/min, carbonization time for 120 min, and carbonization temperature at 300°C/500°C/700°C. The obtained biochar was grinded and sieved through a 100-mesh sieve. The biochar prepared at 300°C/500°C/700°C was denoted as ZLH300, ZLH500, and ZLH700, respectively.

Materials

Potassium nitrate, potassium sodium tartrate, ammonium molybdate, concentrated sulfuric acid, sulfamic acid, potassium dihydrogen phosphate, ascorbic acid, potassium persulfate, hydrochloric acid, sodium hydroxide, sodium chloride, potassium hydrogen phosphate, and sodium hydrogen carbonate were purchased from Aladdin Company. Ammonium chloride, mercury iodide, potassium iodide, and potassium dihydrogen phosphate were provided by Sinopharm Chemical Reagent Co., Ltd. All reagents used in this study was chemical analytical grade without further purification. In this experiment, all solutions were centrifuged using ultrapure water. Ammonia (NH4+-N), nitrate (NO3−-N), and phosphate (PO43−) solution were centrifuged using ammonium chloride, potassium nitrate, and potassium dihydrogen phosphate, respectively.

Instruments

Field emission scanning electron microscope (FE-SEM, JSM-IT300) was employed to observe the morphology of samples. Ultraviolet-visible spectrometer (UV-Vis, QL-5800E) was used to record adsorption spectra of the solution. X-ray diffractometer (D8 Advance) was used to identify the crystal structures of the samples. A Fourier transform infrared spectrometer (FTIR, Nexus) was employed to analyze the functional groups on the samples. BET surface area analyzer (BET, ASAP 2020M) was used to determine the specific surface area and pore size of the samples. Zeta potential analyzer (NanoPlus) was used to determine the zeta potential of the samples. Comprehensive thermal analyzer (STA449F3) was used to analyze carbonization and decomposition procedure of Thalia dealbata Fraser. CHNS/O elemental analyzer (Vario EL cube) and inductively coupled plasma mass spectrometry (ICP-MS7400b) were used to analyze the elemental composition of the sample.

Analysis method of physical and chemical parameters of biochar

Yield of biochar

The mass for precursor and prepared biochar was recorded. The yield of biochar was calculated according to Formula 1:

$$Y=\frac{M_1}{M}\times 100\%$$
(1)

In the formula, Y is the yield of biochar (%); M1 is the mass of biochar after carbonization (g); and M is the mass of Thalia dealbata Fraser before burning and carbonization (g).

Ash content of biochar

The ash content of biochar was determined according to standard “charcoal and charcoal test method (GB/T 17664-1999).”

CEC of biochar

The cation exchange capacity (CEC) of biochar was determined according to standard “Method for measuring the exchange capacity of cation exchange resin (GB/T 8144-2008).”

pH value of biochar

The pH value of biochar was determined according to standard “Wooden activated carbon test method (GB/T 12496.7-199).”

Experiment section

The experimental section included the adsorption kinetics, adsorption isotherms, and effect of pH value on adsorption. In the experiment procedure, 0.1 g of biochar was put into a 200-ml Erlenmeyer flask, and then, 100 ml configured solution was put into Erlenmeyer flask. The adsorption reaction occurred by constant temperature shock box. The temperature and speed for shock box were constant at 20 °C and 180 rpm, respectively. After certain time interval, 2 ml of solution was taken out and filtered using the 0.45-μm microporous membrane. The concentration of NH4+-N, NO3−-N, and PO43− in the filtrate was measured according to standard “Nessler’s reagent colorimetry (GBT 7479-87), phenol disulfonic acid spectrophotometry (GB 7480-1987), and phosphomolybdenum blue colorimetry (GBT 6913-2008),” respectively. All experiments in this study were performed for thrice. Table 1 shows the experimental parameters for adsorption.

Table 1 Experimental parameters
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Adsorption kinetics experiment

The adsorption kinetic of pollutants on biochar included pseudo-first-order, pseudo-second-order, and intraparticle diffusivity models (Formulas 2–4) (Chaudhary et al. 2021; Ghibate et al. 2021; Sohrabi et al. 2021).

Pseudo-first-order model:

$${q}_t={q}_e\left(1-{e}^{\left(-k1t\right)}\right)$$
(2)

Pseudo-second-order model:

$$\frac{t}{q_t}=\frac{1}{{k_2{q}_e}^2}+\frac{t}{q_e}$$
(3)

Intraparticle diffusivity model:

$${Q}_t={k}_w{t}^{0.5}+b$$
(4)

In the formula: qe is the adsorption capacity at equilibrium (mg/g); qt is the adsorption capacity at t (mg/g); k1 is the pseudo-first-order constant; k2 is the pseudo-second-order constant; kw and b were the intraparticle diffusivity constant, respectively.

Adsorption isotherm experiment

The adsorption isotherm of pollutants on biochar included Langmuir and Freundlich models (Formulas 4–5) (Verma et al. 2021; Wang et al. 2021a).

Langmuir model:

$$\frac{\mathrm C}{{\mathrm q}_{\mathrm e}}=\frac{\mathrm C}{{\mathrm q}_{\mathrm m}}+\frac1{{\mathrm q}_{\mathrm m}{\mathrm k}_1}$$
(5)

Freundlich model:

$${\mathrm{lnq}}_{\mathrm e}={\mathrm{lnk}}_{\mathrm f}+\frac{\mathrm{lnC}}{\mathrm n}$$
(6)

In the formula: qm is the theoretical adsorption capacity (mg/g); kl is the Langmuir constant; kf is the Freundlich constant.

Results and discussion

Characterization of Thalia dealbata Fraser and prepared biochar

Figure 1 shows the TG and DTG analysis of Thalia dealbata Fraser biomass. The TG curve could be divided into three stages, namely dehydration stage (25–149 °C), chain scission degradation stage (149–522 °C), and pyrolysis stage (522–1000 °C). The mass loss fraction in the dehydration stage was 5.31% which was ascribed to the evaporation of the water and free water on the surface of the biomass (Wądrzyk et al. 2021). The mass loss fraction in the degradation stage was 86.58%, which was mainly due to the evaporation of the bound water in the biomass and the decomposition of organic matter (Fan et al. 2021). This stage was the main weight loss stage of the biomass. The mass loss fraction in the pyrolysis stage was 0.98%, which was mainly due to the continued decomposition of the remaining organic matter in the biomass and the volatilization of inorganic matter. The weight of the remaining substance is less than 10% of the initial mass when the pyrolysis temperature reached 1000 °C. The value of the DSC curve was greater than > 0 under most conditions, indicating that the exothermic effect was dominated in the process of biomass pyrolysis. Two obvious peaks appear at 325.8 °C and 451.1 °C, indicating that the exothermic effect was the most obvious at this time. The value of the DTG curve was basically greater than <0, indicating that the biomass was a weightless reaction during the pyrolysis process, and a peak occurred at 294.4 °C, indicating that the high weight loss rate.

Fig. 1
figure 1

The TG/DTG analysis of Thalia dealbata Fraser

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Table 2 shows the yield, ash content, pH, and CEC of biochar under different pyrolysis temperatures. As the carbonization temperature increased, the yield and CEC of biochar decreased while ash content and pH of biochar increased. The yield of biochar decreased significantly at 300-500 °C, while the mass loss rate was relatively lower at 500–700 °C. The change in yield and ash content of biochar was ascribed to the decomposition of biomass and the relatively higher proportion of residual inorganics. With the increase of carbonization temperature, the pH value of biochar increased from 7.81 to 10.12. The alkaline dominated pH of biochar was mainly due to the fact that Thalia dealbata Fraser was a wetland emergent plant, which would accumulate a large amount of alkaline salt substances in the water body. As the carbonization temperature increased, the ash content in the biomass increased; meanwhile, the acidic substances (CH4, CO2, CO) in biomass would be volatilized. Therefore, the alkalinity of biochar gradually increased with increasing temperature. The number of functional groups on the surface of biochar was the main factor affecting the CEC of biochar (Rahman et al. 2021). Therefore, the lower CEC was imputed to the reduced oxygen-containing functional groups under higher carbonization temperature.

Table 2 The yield, pH, and CEC of biochar under different pyrolysis temperatures
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Figure 2 shows the zeta potential analysis of biochar by calculating the corresponding pH value when the zeta potential was 0 mV. The pHpzc of ZLH300, ZLH500, and ZLH700 were calculated as 4.47, 5.24, and 6.13, respectively. When the pH value in solution was less than 4.47/5.24/6.13, the surface of ZLH300, ZLH500, and ZLH700 were positively charged; when the pH value was greater than 4.47/5.24/6.13, the surface of ZLH300, ZLH500, and ZLH700 was negatively charged. The pHpzc change of biochar was positively correlated with the pH value on the biochar surface; therefore, the explanation for pHpzc change was also consistent with that of the pH change on biochar.

Fig. 2
figure 2

The zeta potential analysis of biochar

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Tables 3 and 4 show the CNH/O elemental composition and metal elemental content of biochar. With the increasing carbonization temperature, the element content of C and N in biochar increased and decreased consequently, while the element content of O and H gradually decreased. In addition, the ratio of H/C and O+S/C both decreased with increasing carbonization temperature, indicating that biochar has a high degree of aromaticity (Tang et al. 2021). The metal element content of biochar increased with the increase of the carbonization temperature, which was ascribed to the decomposition of organic matter in the biochar, resulting in the enhanced content of ash and inorganic salts.

Table 3 The CNH/O elemental composition of biochar
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Table 4 The metal elemental content of biochar
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Figure 3 and Table 5 show the N2 adsorption–desorption isotherms and BET parameters of biochar, respectively. All the samples exhibited type IV isotherms with H1 hysteresis loop according to IUPAC classification (Yi et al. 2021). With increased carbonization temperature, the surface area and micropore volume of biochar increased obviously while the average aperture was reduced. The BET surface area for ZLH300, ZLH500, and ZLH700 was 3.32, 13.49, and 117.31 m2/g, respectively. Figure 4 shows the SEM scanning images of biochar. The surface of biochar was relatively smooth and exhibited a honeycomb porous structure; when the carbonization temperature reaches 500 °C/700 °C, the structure of biochar changed significantly, and the honeycomb structure had collapsed into the form of flakes and layers.

Fig. 3
figure 3

The N2 adsorption–desorption isotherms of biochar

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Table 5 BET parameters of biochar
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Fig. 4
figure 4

The SEM scanning images of ZLH300 (a, b), ZLH500 (c, d), and ZLH700 (e, f)

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Figure 5 shows the FTIR spectrum of samples. The surface of Thalia dealbata Fraser (Fig. 5a) was rich in functional groups. The characterization peak appeared at 875 cm−1 was ascribed to aromatic heterocyclic ring. The characterization peak appeared at 1117 cm−1 was imputed to C–O and C–C stretching vibration peak (Zhou et al. 2019). The characterization peaks occurred at 1440 cm−1 and 1400 cm−1 were due to –CH2– stretching vibration peak. The characterization peak occurred at 1578 cm−1 and 1558 cm−1 were owing to C=C stretching vibration peak (Li et al. 2020). The characterization peak occurred at 3434 cm−1 was attributed to –OH stretching vibration peak (Sadhu et al. 2021). With the increase of carbonization temperature, there was no obvious shift in the position of the absorption peak, but its intensity was significantly reduced or even disappeared, indicating that high carbonization temperature would reduce the type and number of functional groups on biochar. This result was consistent with other biochars prepared from different carbon sources with different carbonization temperature (Oginni and Singh 2021; Yang et al. 2021b).

Fig. 5
figure 5

FTIR spectrum of Thalia dealbata Fraser (a), ZLH300 (b), ZLH500 (c), and ZLH700 (d)

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Figure 6 shows the XRD patterns of samples. There were some diffraction peaks occurred in XRD patterns of Thalia dealbata Fraser (Fig. 6a), which was corresponding to the characterization peaks of cellulose and lignin (Fan et al. 2021; Wang et al. 2021b). For XRD patterns of biochar, the characteristic peaks of cellulose and lignin disappeared obviously, indicating that lignin and cellulose were destroyed during the carbonization process. In addition, an obvious bulging peak appeared at 2θ = 23°, indicating the amorphous phase structure of biochar (Yang et al. 2021a).

Fig. 6
figure 6

The XRD patterns of Thalia dealbata Fraser (a), ZLH300 (b), ZLH500 (c), and ZLH700 (d)

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Adsorption kinetics analysis

Pseudo-first-order kinetic, pseudo-second-order kinetic, and intra-particle diffusion kinetic models were used to fit adsorption kinetic. Figures 7, 8 and 9 show the kinetic fitting curves of NH4+-N, NO3−-N, and PO43− adsorption on biochar, respectively. Tables 6, 7 and 8 show the kinetic fitting parameters. The adsorption kinetics of pollutants by the three biochars conformed to the quasi-second-order kinetic equation (most of the correlation coefficients R2 > 0.99), indicating that the adsorption of pollutants by biochar was mainly controlled by the chemical adsorption mechanism.

Fig. 7
figure 7

Absorption kinetic of NH4+-N of biochar (a: adsorption quantity; b: quasi-first adsorption kinetic equation; c: quasi-secondary adsorption kinetic equation; d: intraparticle diffusivity)

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Fig. 8
figure 8

Adsorption kinetic of NO3−-N of biochar (a: adsorption quantity; b: quasi-first adsorption kinetic equation; c: quasi-secondary adsorption kinetic equation; d: intraparticle diffusivity)

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Fig. 9
figure 9

The PO43− absorption of biochar (a: adsorption quantity; b: quasi-first adsorption kinetic equation; c: quasi-secondary adsorption kinetic equation; d: intraparticle diffusivity)

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Table 6 The parameters of adsorption kinetic of NO3−-N of different biochars
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Table 7 The parameters of adsorption kinetic of NO3−-N on different biochars
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Table 8 The parameters of adsorption kinetic of PO43− on different biochars
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The intra-particle diffusion model could be divided into two stages, indicating that the adsorption reaction was jointly controlled by the internal and external diffusion stages. In the initial stage of the reaction, the adsorption reaction was faster, and the fitting curve passed through the origin, indicating that the reaction stage was mainly controlled by the internal diffusion process (Islam et al. 2021). In the later stage of the reaction, the adsorption reaction speed slowed down significantly, and the fitting curve did not pass through the origin, indicating that the reaction stage was mainly controlled by the external diffusion process.

According to the parameter qe in the quasi-secondary kinetics, the adsorption capacity of ZLH500 and ZLH700 on pollutants was relatively close, while the adsorption effect of ZLH300 on pollutants was relatively low, which was ascribed to the lower specific surface area and pore volume of ZLH300.

Adsorption isotherm analysis

Langmuir and Freundlich models were used to fit adsorption isotherms. Figures 10, 11 and 12 show the adsorption isotherms curve of NH4+-N, NO3−-N, and PO43− on biochar. Tables 9, 10 and 11 show the adsorption isotherm parameters. The correlation coefficient R2 of Langmuir and Freundlich models was both relatively high, indicating that the two models could goodly fit the adsorption procedure. The adsorption capacity of ZLH500 and ZLH700 was relatively close, which was significantly better than those of ZLH300. According to the Langmuir model, the maximum adsorption capacity of biochar for NH4+-N, NO3−-N, and PO43− is 15.94 mg/g (ZLH500), 5.35 mg/g (ZLH700), and 1.68 mg/g (ZLH700), respectively. According to Freundlich model calculation, all parameter values kf were less than 1, indicating that the adsorption process was belong to preferential adsorption. At the same time, the parameter value 1/n was less than 1, indicating that the adsorption process was a single-layer chemical adsorption dominated behavior.

Fig. 10
figure 10

Adsorption isotherm of NH4+-N (a: adsorption quantity; b: Freundlich; c: Langmuir)

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Fig. 11
figure 11

Adsorption isotherm of NO3−-N (a: adsorption quantity; b: Freundlich; c: Langmuir)

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Fig. 12
figure 12

Adsorption isotherm of PO43− (a: adsorption quantity; b: Freundlich; c: Langmuir)

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Table 9 The parameters of adsorption isotherm of NH4+-N
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Table 10 The parameters of adsorption isotherm of NO3−-N
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Table 11 The parameters of adsorption isotherm of PO43−
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Effect of pH on adsorption of pollutant

Figure 13 shows the effect of pH on NH4+-N, NO3−-N, and PO43− adsorption on biochar. Combining the study of adsorption kinetics and adsorption isotherms, it was known that ZLH500 and ZLH700 had better adsorption effect for pollutants than that of ZLH300. Therefore, the effect of pH on the pollutant adsorption using ZLH500 and ZLH700 was studied. The optimal adsorption effect of NH4+-N and PO43− was reached under neutral and weak alkaline conditions. Acidic conditions were conducive to adsorption of NO3−-N on biochar. According to the results of the previous zeta potential analysis, the pHpzc of ZLH500 and ZLH700 was 5.24 and 6.13, respectively. When the pH value of the solution was less than 5.24/6.13, the surface of ZLH500 and ZLH700 was positively charged; when the pH value was greater than 5.24/6.13, the surface of ZLH500 and ZLH700 was negatively charged. Therefore, in the adsorption process of NH4+-N, there was electrostatic repulsion between biochar and NH4+-N under acidic conditions, while under alkaline conditions, NH4+-N will react with OH− to form relatively stable NH3·H2O, which was not easy adsorbed by biochar; in the adsorption process of NO3−-N, there was electrostatic attraction between biochar and NO3−-N under acidic conditions while electrostatic repulsion between biochar and NO3−-N under alkaline conditions; in the process of PO43− adsorption, under different pH conditions, H2PO4− existed in different forms, relatively stable H2PO4− and H3PO4 dominated in the pH range from 2.15 to 7.20, and HPO42− dominated in the pH range from pH 7.20 to 12.33. The free energy of adsorption of H2PO4− was lower than that of HPO42−, resulting in the poor adsorption effect under strong acidic conditions. In addition, under strong alkali condition, there was electrostatic attraction between the biochar and HPO42−, which also resulted in poor adsorption effect.

Fig. 13
figure 13

The effect of pH on NH4+-N (a), NO3−-N (b), and PO43− (c) adsorption on biochar

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Comparison with other biochar for NH4 +-N, NO3 −-N, and PO4 3− adsorptions

In order to intuitively reflect the nitrogen and phosphorus removal effect of biochar, the adsorption effect of various biochar on nitrogen and phosphorus was compared. Tables 12, 13 and 14 show the theoretical adsorption amount of nitrogen and phosphorus for biochar. In this paper, the maximum theoretical adsorption capacity of NH4+-N, NO3−-N, and PO43− was 15.9 mg/g, 5.31 mg/g and 1.6 mg/g, respectively. Thalia dealbata Fraser based biochar had a comparable adsorption effect on nitrogen and phosphorus with other biochars.

Table 12 Theoretical adsorption amount of NH4+-N by different adsorbates
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Table 13 Theoretical adsorption amount of NO3−-N by different dsorbates
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Table 14 Theoretical adsorption amount of phosphate by different adsorbates
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Discussion for possible adsorption mechanism

Generally, the adsorption behavior of biochar to inorganic pollutants can be explained from the aspects of electrostatic adsorption, ion exchange, and chemical adsorption (Chen et al. 2021; Kong et al. 2021). The electrostatic adsorption behavior was analyzed in detail in the section of pH; the electrostatic attraction behavior was possibly the main adsorption mechanism of NH4+-N and NO3−-N on biochar. Ion exchange behavior can be divided into anion exchange and cation exchange. The adsorption behavior of NH4+-N on biochar was ascribed to the cation exchange. In the above-mentioned biochar composition, it can be found the presence of abundant Ca2+, Mg2+, Fe3+, and Al3+ on the surface of biochar contains. These metal ions with strong ion exchange ability would dissociate on the surface of biochar in solution and undergone ion exchange reaction with NH4+-N (Li and Shi 2022). However, the possible anion on the surface of biochar for anion exchange of NO3--N and PO43− was not been identified. The chemical adsorption behavior of inorganic substances mainly involves precipitation reaction. Biochar also has the accumulation of nutrients such as nitrogen and phosphorus due to the Thalia dealbata Fraser is a wetland perennial emergent plant. Alkaline substance (such as Ca2+/Mg2+) and nitrogen and phosphorus in biochar may chemically react with NH4+-N/ PO43− to form precipitation substances such as struvite (MgNH4PO3) (Cui et al. 2016b). Therefore, the adsorption behavior of NH4+-N/ PO43− on biochar may involve chemical adsorption process.

Conclusion

In this work, Thalia dealbata Fraser–derived biochars were prepared at three different carbonization temperatures (300, 500, and 700 °C) and used as adsorbent for adsorption of nitrogen and phosphorus pollutants. The results indicated that with increased carbonization temperature, the yield of biochar significant decreased and the content of ash increased. In addition, the prepared biochar had higher surface area while the quantity of function group on the surface of biochar reduced obviously under higher carbonization temperature. The adsorption kinetic of pollutants on biochar conformed to the quasi-second-order and intra-particle diffusion models. Langmuir and Freundlich models both could goodly fit the adsorption isotherm procedure. ZLH500 and ZLH700 had better adsorption effect for pollutants than that of ZLH300. The maximum theoretical adsorption capacity of NH4+-N, NO3−-N, and PO43− was 15.9 mg/g, 5.31 mg/g, and 1.6 mg/g, respectively. The pH had played the important role for nitrogen and phosphorus pollutants adsorption. This study indicated the potential of resource utilization of wetland plants and illustrated the effect of carbonization temperatures on the performance of Thalia dealbata Fraser–derived biochar. In future studies, the practical application of Thalia dealbata Fraser–derived biochar in wetlands system can be investigated to achieve the virtuous circle of the ecosystem.