CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL. 62, 2017 

A publication of 

 
The Italian Association 

of Chemical Engineering 
Online at www.aidic.it/cet 

Guest Editors: Fei Song, Haibo Wang, Fang He 
Copyright © 2017, AIDIC Servizi S.r.l. 
ISBN 978-88-95608- 60-0; ISSN 2283-9216 

Preparation, Characterization and Adsorption Performance of 
Reed Biochar 

Zhuo Yang*, Jing Chen 

Hebei University of Environmental Engineering,Qinhuangdao 066102, China 
yangzhuo315566@126.com 

In this article, basic physical and chemical properties and apparent performance of the reed biochar prepared 
under different temperature conditions are studied, and the change of the adsorption time with the change of 
time, initial solution pH value, initial solution Pb2+ concentration for three kinds of biochar have been studied. 
The main study results are given below, in the preparation of these three kinds of biochar, with the rise of 
temperature, the biochar productivity decreases, ash content increases and pH value increases. With the rise 
of pyrolysis temperature, the percentage of the C and N elements of reed biochar increases, while the 
percentage of O and H elements decreases. BET specific surface area, Langmuir specific surface area, T-plot 
microporous specific surface area, and BJH adsorption accumulative specific surface area have manifested 
L500>L700>L300. There is the law of L500>L700>L300 for the quantity of nitrogen adsorption by biochar. The 
adsorption experiment has shown the best adsorption effect of biochar L500 being prepared at 500°C, the 
optimal adsorption condition is pH6, the adsorption time is 150min, and adsorption temperature is 25°C. 

1. Introduction 
Biochar is prepared through pyrolysis and carbonization of biomass in part or total lack of oxygen, has high 
carbon content and developed gap structure, capable of maintaining the nutrient and water content, and is an 
ideal soil conditioner (Lehmann et al., 2006; Liang et al., 2006) Biochar has very high anticorrosion stability, 
superhigh nutrient retaining capability, and has played a huge role in alleviating the greenhouse gas effect, 
soil improvement, environmental pollution alleviation, and resource utilization of solid wastes (Deng, 2012). 
The raw materials for the preparation of biochar come from various sources, and based on the consideration 
of environment-friendly and waste resource recycling and reutilization, the raw materials are mostly taken from 
the waste biomasses, such as wood cuttings, shell, cow dung and the organic wastes generated in the 
industrial and urban life. Such biochar prepared with the waste biomass is used for biological adsorption of the 
environmental recovery due to its excellent performance, so it has attracted more and more emphasis and 
attention (Sohi, 2009). Biochar has the unique surface properties for being the excellent adsorption material. 
From the microstructure, it may be seen that biochar is characterized by being loose and porous and large 
specific surface area, and the functional groups on the surface of biochar include carboxyl group, phenolic 
hydroxyl group and acid anhydride groups. These make biochar have good adsorption characteristics, and 
can influence and change the migration, transformation and ecological effect of the pollutants in the 
environment, and reduce the environmental risks (Jiang et al., 2013). 
The basic nature of biochar is mainly influenced by the factors, such as raw materials, preparation 
temperature and preparation time. Due to the difference in raw materials, technical process and pyrolysis 
conditions, biochar has manifested very wide diversity in the physical and chemical properties, such as 
structural composition, pH, ash content, water content and specific surface area. Different biomass materials 
contain different specific gravity of cellulose, semi-cellulose and lignin, have different tissue structures and the 
porous structures of the carbides vary very significantly (Lehmann, 2007). At present, it is universally held in 
the academic field that the raw materials and pyrolysis temperature of biochar have the largest impact on the 
carbon physical and chemical properties and environmental functions, and the biochar precursor raw material 
constituents are the basis for deciding the biochar composition and nature, while the impact of biochar 

                                

 
 

 

 
   

                                                  
DOI: 10.3303/CET1762208 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Please cite this article as: Zhuo Yang,  Jing Chen, 2017, Preparation, characterization and adsorption performance of reed biochar, Chemical 
Engineering Transactions, 62, 1243-1248  DOI:10.3303/CET1762208   

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pyrolysis temperature on its environment application characteristics is always the hot point in study (Xie, 
2011). 
Reed is the typical wetland plant, and as a gramineous tall and perennial emergent aquatic and herbaceous 
plant, it has very wide adaptability and very strong stress resistance, and it is characterized by long growth 
season, quick growth and high production. Reed has very large aboveground biomass, and in Baiyangdian 
Reed Wetland, the aboveground dry mass of the reed is 6,000~7,500kg/hm2. But, due to lack of economically 
efficiency resource utilization technology, the reed in the wetland system cannot be removed in a timely 
manner, and in case of natural decay and decomposition, the pollutants and nutrients will be released into the 
wetland system, resulting in the secondary pollution. Since reed is characterized by fast growth and large 
biomass, being suitable for acquisition and having low cost, it is the plant resource suitable for being 
processed into the biochar. 
In this study, reed is prepared by using the raw materials through pyrolysis in different temperatures for the 
preparation of biochar, thus revealing the rules between biochar characteristics and preparation conditions, 
such as pyrolysis temperature and pyrolysis time, through the representation of the biochar characteristics, 
thus providing the basic evidence for the quotation and promotion of biochar. Besides, in this study, the 
adsorption performance and principle of biochar to Pb are also analyzed, and in this article, the new materials 
are provided for the environmental repair. At the same time, the adsorption performance and law of biochar to 
Pb has been analyzed. This article has developed the new technology of resource utilization for the wetland 
plant, and provided new information for the environmental recovery. 

2. Materials and method 
2.1 Preparation of biochar 

The reed, as the test plant, is taken from Red Beach National Natural Reserve in Dawa County, Panjin City, 
Liaoning Province, and the sampling place is situated in the wetland of Erjiegou Town. Clean the plant, and 
then air-dry it for 72h. Then crush it, and place it into the electric heating oven for 1h drying. When it is cooled 
down to the room temperature, a proper amount of precursor raw material is weighed with the electric balance 
(accurate to 0.01g) into the combustion boat (self-produced) and then transferred into tube-type vacuum 
furnace for pyrolysis. Set different carbonization temperature (300°C, 500°C, 700°C) for carbonization, with 
the temperature increment of 5°C/min, and keep the temperature for 2h for each increment. Fill the high-purity 
nitrogen at the flow rate of 0.7L⁄min in the whole process. Let it cool down, and grind the sample, let it pass the 
100-mesh sieve, thus obtain the biochar finished product, and place it into the sealed bag for storage. Mark 
them as the reed biochar (L300, L500, L700) respectively. 

2.2 Method of characterization for the characteristics of biochar 

Determine productivity of biochar: weigh the biochar before and after the treatment. Th ratio of the sample 
mass after the carbonization to the dry weight of raw material is the productivity; 
Determine ash content of biochar: weigh about 1.0g biochar sample passing 100-mesh (accurate to 0.01mg), 
lay it flatly in the bottom of the porcelain crucible, place the open side into the muffle furnace, for ashing at 
800°C for 4h, let it cool down to the room temperature, take it out and weigh it. 
Calculate the ash content with the formula: A=((G2-G1)/G)x100% 
Where, A is the percentage of ash content in the sample, %; G is the content of biochar before the ignition, g; 
G1 is the mass of the empty crucible, g; G2 is the ash content and crucible mass, g. 
Determine the pH value of biochar: refer to the method in Masulili (2010) for the determination method of 
biochar pH, that is, dilute biochar sample with the deionized water, for the preparation of 1% biochar 
suspension. Heat it to 90°C and fully stir it for 20min, so that the soluble constituents in biochar can be 
dissolved in the aqueous solution, finally let it cool down to the room temperature, and determine the 
corresponding pH value with pH meter. Determine the content percentage of C, H, N and O elements in reed 
biochar with vario Micro cube element analyzer (Elementar (Germany), model: vario Micro cube). According to 
BET method, determine the specific surface area and pore size distribution of reed biochar with the specific 
surface area and pore size distribution analyzers under the conditions of liquid nitrogen temperature (77K). 
Add the biochar passing the 100-mesh sieve into water, then add certain quantity of sodium oxalate to 
dissolve it, separate and suspend it in CNC ultrasonic cleaner, and take the suspension for the determination 
of the potential with ZETA potentiometric analyzer (brand: MALVERN, model: Nano-Z). Make the gold plating 
on a small amount of biochar samples, and attach them on the sample table, then observe the shape and 
surface characteristics of the sample with the scanning electron microscope (SEM). Determine the infrared 
spectrum of biochar with Fourier transformation infrared spectrometer. 

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2.3 Biochar adsorption capability and law 

(1) Adsorption dynamic test 
Weigh 0.1000g biochar sample into 150mL triangular flask, add 50 mL 20 mg·L-1 Pb2+ ion solution, where the 
concentration of background electrolyte NaNO3 is 0.01mol·L

-1. Regulate the pH value of the solution to 5.5 by 
using the diluted HNO3 and NaOH, vibrate it at constant temperature (25°C, 200 r·min

-1), determine the 
adsorption quantity of Pb2+ for the sampling at 5, 10, 15, 20, 30, 40 min, and 1, 2, 8, 16, 24, 30, 48 h, taking 
that without addition of biochar as the positive control, and the deionized water as the negative control. 
(2) The influence of initial pH value of the solution on the adsorption rate 
Weigh 0.1000g biochar sample into 150 mL triangular flask, where the concentration of background electrolyte 
NaNO3 is 0.01 mol·L

-1, the initial mass concentration is 20 mg·L-1 Pb2+ solution 50mL. Regulate pH value to 2, 
3, 4, 5, 6, 7, vibrate it at constant temperature (25°C, 200 r·min-1) for 24h, filter it, and determine the final pH of 
the suspension, regulate the filtrate pH<2, determine the concentration of Pb2+, taking that without addition of 
biochar as the positive control, and the deionized water as the negative control. 
(3) Isothermal adsorption 
Weigh 0.1000g biochar sample into 150 mL triangular flask. Where the initial pH value of the solution is 5.5, 
and the concentration of background electrolyte NaNO3 is 0.01 mol·L

-1. Regulate Pb2+ mass concentration as 
2.0, 5.0, 10.0, 20.0, 40.0, 80.0 mg·L-1 respectively, vibrate it at constant temperature for 24 h (200 r·min-1), 
and determine the isothermal adsorption of biochar to Pb2+ at 25°C. Take the sample, filter it, regulate the 
filtrate pH<2, determine the concentration of Pb2+. Take that without addition of biochar as the positive control, 
and the deionized water as the negative control. Calculate the adsorption of biochar to Pb2+ according to initial 
concentration and balance concentration of Pb2+. Repeat the above tests for twice. 
(4) Orthogonal test 
According to the optimal single-factor test results, draft the three-factor and three-level orthogonal test, and 
survey the optimal adsorption conditions of the biochar. 

3. Results and analysis 
3.1 Reed biochar apparent performance and physical and chemical property analysis 

(1) Productivity, ash content and pH value of reed biochar 
The productivity, ash content and pH value of biochar at different pyrolysis temperature are shown in Table 1. 
With the rise of temperature, the biochar productivity decreases, ash content increases, and pH value rises. 
With respect to productivity, there is L300>L500>L700; with respect to ash content, there is L300<L500<L700; 
and with respect to pH value, there is L300<L500<L700. It indicates that with the rise of pyrolysis temperature, 
the material pyrolysis increases, the biochar productivity decreases, and ash content is gradually 
accumulated. At low temperature, high productivity of biochar is obtained because of low concentration of the 
fatty hydrocarbon substances in the raw material, and small escape of CH4, H2 and CO (Yang, 2007). At 
300°C, biochar productivity is 26.24%, and when temperature rises to 700°C, the productivity decreases to 
18.96%, with the decrease rate of about 28%. The biochar of the material has significant mass loss at 
500°C~700°C, while has small mass loss at 300°C~500°C, so it may be inferred that, 500°C~700°C is the key 
interval for the mass loss of raw materials. With the rise of the pyrolysis temperature, pH value increases from 
6.44 to 8.98, with the increase rate of 39%. As the soil conditioner, biochar can improve the pH value of the 
soil, and the increase of pH value in soil can inhibit the release of some greenhouse gases. Therefore, it is 
possible to alleviate the global warming trend by adding biochar into the soil. 

Table 1: Productivity, ash content and pH value of biochar 

Reed biochar Productivity (%) Ash content (%) pH value 
L300 26.24 6.10 6.44 
L500 25.10 11.24 7.72 
L700 18.96 11.43 8.98 

 
(2) Biochar element composition analysis 
The element composition and atomic ratio of reed raw material and biochar are shown in Table 2. With the 
rise of pyrolysis temperature, the percentage content of C and N elements of reed biochar increases, while the 
percentage content of O and H elements decreases. After pyrolysis of the raw material, the percentage 
content of C and N elements increases by comparison with that in the raw material, and the percentage 
content of O and H elements decreases by comparison with that in the raw material. By comparison with that 
at 300°C, that at 700°C has the percentage content of C element increased by 46%, percentage content of N 
element increased by 44%, percentage content of O element decreased by 85%, and percentage content of H 

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element decreased by 73%. The main reason is that a large amount of O element and H element has been 
lost due to the dehydration reaction, decarboxylic reaction and dehydroxylation reaction of cellulose, semi-
cellulose and lignin in the reed raw material during the pyrolysis. A large amount of CO2 has been produced 
during the pyrolysis of biomass, with the volatilization of some micromolecular organisms, and with the loss of 
some C element. But in general, more O element and H element has been lost, and the general trend is that 
percentage content of C element will increase with the rise of pyrolysis temperature. Kuhlbusch et al. defined 
H/C≤0.2 for black carbon (Graetz, 2003) and Graetz et al. thought that the biochar formed in high temperature 
had H/C≤0.5 (Schmidt and Noack, 2000). In this study, the biochar H/C is lower than 0.2 at all of these three 
temperatures, and with the rise of the pyrolysis temperature, H/C and O/C will decrease, indicating that the 
reed biochar products have high aromaticity and degree of curing, and good characteristics. 

Table 2: Element composition and atomic ratio of reed biochar at different temperatures 

Reed biochar C(%) H(%) N(%) O(%) H/C N/C O/C 

Raw material 44.80 6.20 0.41 43.25 0.14 0.01 0.97 
L300 55.81 5.40 0.52 30.23 0.10 0.01 0.54 
L500 74.46 3.12 0.68 9.09 0.04 0.01 0.12 
L700 81.38 1.45 0.75 4.61 0.02 0.01 0.06 

 
(3) Reed biochar specific surface area, microporous volume and pore size distribution 
Refer to Table 3 for the specific surface area and average pore size of reed biochar under different 
preparation temperatures. The study has shown, BET specific surface area, Langmuir specific surface area, 
T-plot microporous specific surface area, and BJH adsorption accumulative specific surface area have been 
L500>L700>L300, and BET average pore size is L700>L300>L500. This has shown that at 500°C, the 
prepared biochar has large specific surface area, and strong adsorption potential. 

Table 3: Reed biochar specific surface area and average pore size 

 

BET 
specific 
surface area 
(m2/g) 

Langmuir 
 specific 
surface area 
(m2/g) 

T-plot 
 microporous specific 
surface area 
(m2/g) 

BET 
Average 
pore size 
 (nm) 

BJH 
 Adsorption accumulative 
specific surface area 
(m2/g) 

L300 1.2293 1.7923 0.0217 5.9316 0.420 
L500 2.4487 3.5441 2.3531 5.1236 1.074 
L700 1.4810 1.9811 0.0383 6.2375 0.534 

 
(4) Adsorption and desorption of reed biochar to nitrogen under different pressures 
The adsorption and desorption of the reed biochar prepared at different temperatures to nitrogen under 
different pressures have the similar laws, with the details shown in Fig. 1-Fig. 3. From the adsorption of 
biochar to nitrogen, it may be seen that, L500>L700>L300, which shows that at 500°C, the prepared biochar 
has good adsorption performance.  

                       
Figure 1: Adsorption and desorption of L300 to            Figure 2: Adsorption and desorption of L500 to 
nitrogen at different pressures                                      nitrogen at different pressures 

 
Figure 3: Adsorption and desorption of L700 to nitrogen at different pressures 

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(5) Potentiometric analysis 
From Table 4, it may be seen that, there is the negative charge on the surface of three kinds of biochar, L500 
has the biggest charge, and L700 has the smallest charge. The positive/negative and size of the charge on 
the surface of the biochar has decided the electric neutralization effect. So these three kinds of biochar have 
the capability of adsorbing positive charges, where L500 might have the highest adsorption capability.  

Table 4: Potential of reed biochar 

 Zata potential (mV) Mob (µmcm/Vs) Conductivity(mS/cm) 
L300 -34.9 -2.735 -0.0559 
L500 -35.4 -2.777 -0.0715 
L700 -34.5 -2.702 -0.0354 

3.2 Reed biochar adsorption performance analysis 

(1) Influence of time, initial pH value of the solution and Pb2+ concentration on the biochar adsorption 
capability 
Figure. 4-Figure. 6 have displayed the law for the change of adsorption rate of reed biochar prepared under 
different temperatures with the reaction time, initial solution pH value and Pb2+ concentration. From Fig. 4, it 
may be seen that, with the change of time, the adsorption rate of these three kinds of biochar is 
L500>L300>L700. With the extension of the time, the adsorption rate gradually increases, and after two hours, 
it basically tends to be stable. The maximum adsorption rate of the biochar to Pb2+ is up to 48%. From Fig. 5, 
it may be seen that, due to the difference of pH values of the initial solution, these three kinds of biochar have 
the adsorption rate L500>L700>L300. With the increase of pH value of the initial solution, the adsorption rate 
gradually increases, and when pH value reaches 6~7, the adsorption rate reaches the maximum level. The 
maximum adsorption rate of biochar to Pb2+ is up to 49%. From Fig. 6, it may be seen that, with the increase 
of Pb2+ concentration in initial solution, the adsorption rate increases, and these three kinds of biochar have 
the adsorption rate L500>L700>L300. When the Pb2+ concentration reaches 20mgL-1, the adsorption rate 
reaches the maximum level, and then slightly decreases. The maximum adsorption rate of biochar to Pb2+ is 
up to 46%. 

                              

Figure 4: Influence of the time change on               Figure 5: Influence of the change of initial solution pH value 
on the reed biochar adsorption rate                      the reed biochar adsorption rate 

 

Figure 6: Influence of the Pb2+ concentration change on reed biochar adsorption rate 

(2) Orthogonal test result analysis 
This experiment is the three-factor and three-level orthogonal test for three kinds of biochar, where the three 
factors are temperature, time and pH value, and three levels are the optimal levels selected from the single 
factor experiments. The final experiment results have shown that biochar L500 prepared at 500°C has the 
best adsorption effect, and the optimal adsorption condition is pH6, adsorption time is 150min, and adsorption 
temperature is 25°C. 

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4. Conclusion and discussion 
Biomass is mainly composed of cellulose, semi-cellulose, lignin and a small amount of organic extract and 
inorganic minerals. These constituents vary due to the types of biomass, and in addition, for specific biomass, 
the component proportion is highly influenced by the soil type, climatic conditions and collection time. the 
decomposition temperature of semi-cellulose is 200~260°C, the decomposition temperature of cellulose is 
240~350°C, and the decomposition temperature of lignin is 280~500°C (Hamelinck, 2005). Therefore, the 
percentage of these constituents in the raw material influences the biochar activity and the structural change 
in the pyrolysis. For the given raw material, the factors influencing the biochar include heating rate, maximum 
pyrolysis temperature, maximum pyrolysis temperature retention time, pretreatment and device to be used, 
where the critical factor is the maximum pyrolysis temperature, because the release of the volatile and the 
forming and volatilization of the intermediate melt is closely related to the temperature. In this study, when the 
temperature rises to 500°C, the pyrolysis of the lignin structure has resulted in the sharp decrease of the 
biochar productivity to about 25.1%. Thus, when the characteristics of biochar meet its use, it shall be possible 
to realize the maximization of the productivity. While in the maximization of the productivity, it is required to 
determine the optimal pyrolysis temperature according to the type of the raw material. The adsorption rate of 
the biochar will change with the external conditions, and it is required to explore the external conditions for 
biochar adsorption rate to reach the maximum level. 
The final experiment results in this study are given below: in the preparation of these three kinds of biochar, 
with the rise of temperature, the biochar productivity decreases, ash content increases and pH value 
increases. With the rise of pyrolysis temperature, the percentage of the C and N elements of reed biochar 
increases, while the percentage of O and H elements decreases. BET specific surface area, Langmuir specific 
surface area, T-plot microporous specific surface area, and BJH adsorption accumulative specific surface area 
have manifested L500>L700>L300. There is the law of L500>L700>L300 for the quantity of nitrogen 
adsorption by biochar. The adsorption experiment has shown the best adsorption effect of biochar L500 being 
prepared at 500°C, the optimal adsorption condition is the optimal adsorption condition is pH6, the adsorption 
time is 150min, and adsorption temperature is 25°C. 

Acknowledgments  

Science and Technology Research Project for Institutions of Higher Learning in Hebei Province under 
Department of Education of Hebei Province in 2017- “Study on the restoring effect of biochar immobilized 
microorganism on the oil polluted by heavy metals” (No. ZD2017025).  

References 

Deng X., 2012, Effects of Giant Reed Biochar on Nitrogen bioavailability in the Agricultural Soil, Ocean 
University of Chin, 6. 

Graetz R.D., Skjemstad J.O., 2003, The charcoal sink of biomass burning on the Australian continent, CSIRO 
Atlmospheric Research, 64. 

Hamelinck C.N., Hooijdonk G.V., Faajj A., 2005, Ethanol from lignocellulosic biomass, techno-economic 
performance in short, middle and long term, 28 (4), 384-410, DOI: 10.1016/j.biombioe.2004.09.002 

Jiang Y.Y., Hu X.M., Jin W.B., 2013, Advances on Absorption of Heavy Metals in the Waste Water by Biochar, 
Hubei Agricultural Sciences, 52 (13), 2985-2988. 

Lehmann J., 2007, Bio-energy in the black, The Ecological Society of America, 5 (7), 381-387, DOI: 
10.1890/1540-9295(2007)5[381:BITB]2.0.CO;2 

Lehmann J., Gaunt J., Rondon M., 2006, Biochar sequestration in terrestrial ecosystem, Mitigation and 
Adaptation Strategies for Global Change, (11), 403-427. 

Liang B.Q., Lehmann J., Solomon D., Kinyangi J., Grossman J.M., O’Neill B., Skjemstad J.O., Thies J.E., 
Luizão F.J., Petersen J., Neves E.G., 2006, Black Carbon increases cation exchange capacity 

Schmidt M.W.I., Noack A.G., 2000, Black Carbon in Soils and Sediments, Analysis, Distribution, Implications, 
and Current Challenges, Global Biogeochemica Cycles, 14, DOI: 10.1029/1999GB001208 

Sohi S., Loez-Capel E., Krull E., Bol R., 2009, Biochars roles in soil and climate change, A review of research 
needs, UK, CSIRO Land and Water Science Report, 64.  

Xie Z.B., Liu Q., Xu Y.P., Zhu C.W., 2011, Advances and Perspectives of Biochar Research, Soils, 43 (6), 
857-861. 

Yang H., Yan R., Chen H., Lee, D.H., Zheng C.G., 2007, Characteristics of hemicellulose, cellulose and lignin 
pyrolysis, Fuel, 86 (12-13), 1781-1788, DOI: 10.1016/j.fuel.2006.12.013 

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