CoChat
Sign Up
Cited by 29Adsorption and biosorption for pollutant removalThermochemical Biomass Conversion ProcessesEnvironmental remediation with nanomaterials

Effect of temperature and duration of pyrolysis on spent tea leaves biochar: physiochemical properties and Cd(II) adsorption capacity

Open access
Yang, Zhanbiao, Liu, Xincong, Zhang, Mengdi, Liu, Lixia, Xu, Xiaoxun, Xian, Junren, Cheng, Zhang·2020·Water Science and Technology
DOI 10.2166/wst.2020.309
Open this paper in CoChat — free accountOpen PDF

Abstract

We analyzed the effects of pyrolysis temperature and duration on the physiochemical properties and Cd(II) adsorption capacity of spent tea leaves (STL) biochar. The STL biochar was produced by pyrolysis at 300, 400, 500 and 600 °C for 1 and 2 h. The pyrolysis temperature was positively correlated to the ash content, pH, electrical conductivity, specific surface area (SBET), pore volume (PV) and C content, and negatively with the total yield, O, H and N content, and the O/C and H/C atomic ratios. Furthermore, the surface porosity of STL biochar increased, the density of oxygen-containing functional groups decreased, and the formation of aromatic structures was enhanced at higher pyrolysis temperatures. The adsorption of Cd(II) onto STL biochar fitted with the pseudo-second-order kinetics and Langmuir isotherms model. The STL biochar produced at 600 °C for 2 h showed the maximum Cd(II) adsorption capacity of 97.415 mg/g. In addition, Cd(II) adsorption was mainly physical and occurred in monolayers. Thus, STL biochar is a suitable low-cost adsorbent for wastewater treatment.

Integrity signals

Registry

Crossref · 10.2166/wst.2020.309

Cites

54 of 54 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 3 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    The density of oxygen-containing functional groups on STL biochar decreased with increasing pyrolysis temperature.

    “Furthermore, the surface porosity of STL biochar increased, the density of oxygencontaining functional groups decreased, and the formation of aromatic structures was enhanced at higher pyrolysis temperatures.”
    • Also stated in: § Characterization of surface functional groups · plain
      “As shown in Figure 6, the density of the oxygen-containing functional groups, such as hydroxyl (-OH), carboxyl (-COOH) and phenols (C-OH), decreased with increasing temperature.”
    Quote in the paperSubstantial claim
  • Findingown data

    The adsorption of Cd(II) onto STL biochar fitted the pseudo-second-order kinetics model.

    “The adsorption of Cd(II) onto STL biochar fitted with the pseudosecond-order kinetics and Langmuir isotherms model.”
    • Also stated in: § Adsorption kinetics · plain
      “According to the R 2 values, the pseudo second-order rather than first-order kinetic model was representative of the Cd(II) sorption kinetics on STL biochars (Table 3).”
    • Also stated in: § CONCLUSION · plain
      “Biochar produced at 600 C for 2 hours adsorbed the largest amount of Cd(II), and the sorption kinetics closely followed the pseudo-second-order model.”
    Quote in the paperSubstantial claim
  • Findingown data

    The surface porosity of STL biochar increased at higher pyrolysis temperatures.

    “Furthermore, the surface porosity of STL biochar increased, the density of oxygencontaining functional groups decreased, and the formation of aromatic structures was enhanced at higher pyrolysis temperatures.”
    Quote in the paperSubstantial claim
  • Findingown data

    The relationship between ash content and pH of STL biochar followed an exponential trend (Adj.R2 = 0.936).

    “As shown in Figure 2, the relationship between ash content and pH of STL biochar followed an exponential trend (Adj.R 2 ¼ 0.936).”
    Quote in the paperNot a substantial claim
  • Findingown data

    The interaction between pyrolysis temperature and duration did not have a statistically significant effect on the yield, ash content, pH, EC, or CEC of STL biochar.

    “Temperature × duration | | 1.569 | 0.561 | 3.679 | 0.037 | 0.798”
    Quote in the paperSubstantial claim
  • The quote only partly states this claim. 8
  • May combine two claims. 28

  • The quote only partly states this claim.

    Findingreasoning

    Cd(II) adsorption increased as the solution temperature increased from 20 to 40 C.

    “The results indicated that Cd(II) adsorption increased as the temperature increased.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The adsorption rates increased significantly at Cd(II) concentration below 60 mg/L, and decreased thereafter.

    “As shown in Figure 8(c) and 8(d), the adsorption rates increased significantly at Cd(II) concentration below 60 mg/L, and decreased thereafter.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingreasoning

    Pyrolysis temperature is positively correlated with the specific surface area (S_BET) of STL biochar; S_BET was extremely low below 500 C (1.64-8.75 m2/g) and increased to 62.52-67.10 m2/g at 600 C.

    “The pyrolysis temperature was positively correlated to the ash content, pH, electrical conductivity, specific surface area (S BET ), pore volume (PV) and C content, and negatively with the total yield, O, H and N content, and the O/C and H/C atomic ratios.”
    • Also stated in: § Surface characteristics and micro morphology · plain
      “The S BET of STL biochar pyrolyzed at temperatures below 500 C were extremely low (1.64-8.75m 2 /g), and increased to 62.52-67.10m 2 /g at 600 C (Figure 4).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Pyrolysis temperature is negatively correlated with the H content of STL biochar; H content decreased from 3.71 to 1.78% as temperature increased from 300 to 600 C.

    “The pyrolysis temperature was positively correlated to the ash content, pH, electrical conductivity, specific surface area (S BET ), pore volume (PV) and C content, and negatively with the total yield, O, H and N content, and the O/C and H/C atomic ratios.”
    • Also stated in: § Characteristics of STL biochar · plain
      “The average C content increased from 64.26 to 81.44%, while that of H, O and N respectively decreased from 3.71 to 1.78%, 23.76 to 14.43% and 2.29 to 0.78% as the pyrolysis temperature was increased from 300 to 600 C.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingreasoning

    Pyrolysis temperature is negatively correlated with the H/C atomic ratio of STL biochar; the H/C ratio was 62.24% lower in biochar produced at 600 C compared to 300 C.

    “The pyrolysis temperature was positively correlated to the ash content, pH, electrical conductivity, specific surface area (S BET ), pore volume (PV) and C content, and negatively with the total yield, O, H and N content, and the O/C and H/C atomic ratios.”
    • Also stated in: § Characteristics of STL biochar · plain
      “In addition, the O/C and H/C ratios were respectively 52.25% and 62.24% lower in the biochar produced at 600 C compared to that at 300 C, which can be attributed to a greater degree of dehydration and decarboxylation at high temperatures (Ahmad et al.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    STL biochar produced at 600 C for 2 h reached the adsorption equilibrium faster and adsorbed the largest amount of Cd(II) compared to other biochar samples.

    “The STL biochar produced at 600 C for 2 h reached the adsorption equilibrium faster and adsorbed the largest amount of Cd(II) compared to other biochar samples.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Pyrolysis temperature is positively correlated with the pH of STL biochar; average pH increased from 5.75 at 300 C to 7.2, 7.38 and 7.44 at 400, 500 and 600 C respectively.

    “The pyrolysis temperature was positively correlated to the ash content, pH, electrical conductivity, specific surface area (S BET ), pore volume (PV) and C content, and negatively with the total yield, O, H and N content, and the O/C and H/C atomic ratios.”
    • Also stated in: § Characteristics of STL biochar · plain
      “The average pH of STL biochar increased from 5.75 at 300 C to 7.2, 7.38 and 7.44 at 400, 500 and 600 C respectively (Table 1).”
    Quote in the paperNot a substantial claim

  • May combine two claims. The quote only partly states this claim.

    Findingown data

    Pyrolysis temperature is positively correlated with the pore volume (PV) of STL biochar; PV was maximum (0.0301 cm3/g) in STL biochar produced at 600 C for 2 h.

    “The pyrolysis temperature was positively correlated to the ash content, pH, electrical conductivity, specific surface area (S BET ), pore volume (PV) and C content, and negatively with the total yield, O, H and N content, and the O/C and H/C atomic ratios.”
    • Also stated in: § Surface characteristics and micro morphology · plain
      “Likewise, PV value was maximum (0.0301 cm 3 /g) in the STL biochar produced at 600 C for 2 h (Figure 4).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Pyrolysis temperature is positively correlated with the electrical conductivity (EC) of STL biochar; EC increased at higher temperatures and was maximum in samples pyrolyzed at 600 C for 2 h.

    “The pyrolysis temperature was positively correlated to the ash content, pH, electrical conductivity, specific surface area (S BET ), pore volume (PV) and C content, and negatively with the total yield, O, H and N content, and the O/C and H/C atomic ratios.”
    • Also stated in: § Characteristics of STL biochar · plain
      “the electrical conductivity (EC), which reflects the total amount of dissolved salts in biochar, also increased at higher temperatures (Table 1; P < 0.01) and was maximum in samples pyrolyzed at 600 C for 2 h.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Pyrolysis temperature is positively correlated with the C content of STL biochar; average C content increased from 64.26 to 81.44% as temperature increased from 300 to 600 C.

    “The pyrolysis temperature was positively correlated to the ash content, pH, electrical conductivity, specific surface area (S BET ), pore volume (PV) and C content, and negatively with the total yield, O, H and N content, and the O/C and H/C atomic ratios.”
    • Also stated in: § Characteristics of STL biochar · plain
      “The average C content increased from 64.26 to 81.44%, while that of H, O and N respectively decreased from 3.71 to 1.78%, 23.76 to 14.43% and 2.29 to 0.78% as the pyrolysis temperature was increased from 300 to 600 C.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    The adsorption rates decreased thereafter and approached equilibrium by 48 h.

    “The adsorption rates decreased thereafter and approached equilibrium by 48 h.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Pyrolysis temperature is positively correlated with the ash content of spent tea leaves (STL) biochar; ash content increased from 5.84 to 17.89% as temperature increased from 300 to 600 C.

    “The pyrolysis temperature was positively correlated to the ash content, pH, electrical conductivity, specific surface area (S BET ), pore volume (PV) and C content, and negatively with the total yield, O, H and N content, and the O/C and H/C atomic ratios.”
    • Also stated in: § Characteristics of STL biochar · plain
      “The ash content of STL biochar increased from 5.84 to 17.89% with increasing pyrolysis temperature (Table 1) due to loss of organic matter and accumulation of inorganic compounds, and showed an exponential curve (Figure 1(b); Adj.R 2 ¼ 0.980).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Pyrolysis duration had a statistically significant effect on the yield and CEC of STL biochar, but not on ash content, pH, or EC.

    “duration | | 7.661* | 3.679 | 1.17 | 1.701 | 14.965*”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The maximum Cd(II) adsorption capacity of STL biochar produced at 600 C for 2 h was 1.38-1.63, 1.07-1.26 and 1.01-1.14 times greater than that of biochar samples produced at 300, 400 and 500 C respectively.

    “According to the saturation threshold of the best matching model, the STL biochar produced at 600 C for 2 h showed the maximum Cd(II) adsorption capacity of 97.415 mg/g, which was 1.38-1.63,1.07-1.26and 1.01-1.14times greater than that of biochar samples produced at 300, 400 and 500 C respectively.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    SEM micrographs of STL biochar showed a smoother surface and pores blocked with volatile organic compounds at low pyrolysis temperatures.

    “Consistent with the above results, the SEM micrographs of STL biochar showed a smoother surface and pores blocked with volatile organic compounds at low pyrolysis temperatures (Figure 5(a), 5(b), 5(e), 5(f)).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Pyrolysis temperature is negatively correlated with the total yield of STL biochar; yield decreased significantly from 52.17% to 26.71% as temperature increased from 300 to 600 C.

    “The pyrolysis temperature was positively correlated to the ash content, pH, electrical conductivity, specific surface area (S BET ), pore volume (PV) and C content, and negatively with the total yield, O, H and N content, and the O/C and H/C atomic ratios.”
    • Also stated in: § Characteristics of STL biochar · plain
      “Consistent with this, the yield of STL biochar decreased significantly from 52.17% to 26.71% as the temperature was increased from 300 to 600 C (Table 1; P < 0.01).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingreasoning

    The cation exchange capacity (CEC) of STL biochar ranged from 107.97 to 407.79 cmol/kg and was higher at lower temperatures (300 and 400 C).

    “The CEC ranged from 107.97 to 407.79 cmol/kg, and was higher at lower temperatures (300 and 400 C).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Cd(II) adsorption increased in acidic solutions of pH 2-5 and decreased as the acidity diminished, with optimal uptake seen at pH 5.

    “Specifically, Cd(II) adsorption increased in acidic solutions of pH 2-5 and decreased as the acidity diminished, with optimal uptake seen at pH 5.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Pyrolysis at 500 and 600 C significantly increased the surface cracks and holes of STL biochar, indicating a highly porous structure.

    “However, pyrolysis at 500 and 600 C significantly increased the surface cracks and holes, indicating a highly porous structure.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingnone given

    Over the studied pH range, STL biochar produced at 600 C showed the maximum adsorption of Cd(II) and that produced at 300 C showed the least adsorption capacity.

    “Over the studied pH range, STL biochar produced at 600 C showed the maximum adsorption of Cd(II) and that produced at 300 C showed the least adsorption capacity.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingreasoning

    Pyrolysis temperature is negatively correlated with the O/C atomic ratio of STL biochar; the O/C ratio was 52.25% lower in biochar produced at 600 C compared to 300 C.

    “The pyrolysis temperature was positively correlated to the ash content, pH, electrical conductivity, specific surface area (S BET ), pore volume (PV) and C content, and negatively with the total yield, O, H and N content, and the O/C and H/C atomic ratios.”
    • Also stated in: § Characteristics of STL biochar · plain
      “In addition, the O/C and H/C ratios were respectively 52.25% and 62.24% lower in the biochar produced at 600 C compared to that at 300 C, which can be attributed to a greater degree of dehydration and decarboxylation at high temperatures (Ahmad et al.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Pyrolysis temperature is negatively correlated with the O content of STL biochar; O content decreased from 23.76 to 14.43% as temperature increased from 300 to 600 C.

    “The pyrolysis temperature was positively correlated to the ash content, pH, electrical conductivity, specific surface area (S BET ), pore volume (PV) and C content, and negatively with the total yield, O, H and N content, and the O/C and H/C atomic ratios.”
    • Also stated in: § Characteristics of STL biochar · plain
      “The average C content increased from 64.26 to 81.44%, while that of H, O and N respectively decreased from 3.71 to 1.78%, 23.76 to 14.43% and 2.29 to 0.78% as the pyrolysis temperature was increased from 300 to 600 C.”
    Quote in the paperNot a substantial claim

  • May combine two claims. The quote only partly states this claim.

    Findingown data

    Increasing pyrolysis temperature from 300 to 600°C increased the carbon content and C/N ratio and decreased the H, O, N, O/C, and H/C ratios of STL biochar.

    “C | (%) | 62.55 | 65.96 | 69.68 | 70.82 | 72.47 | 74.15 | 80.70 | 82.18”
    • Also stated in: § CONCLUSION · plain
      “H | (%) | 3.86 | 3.55 | 3.23 | 3.06 | 2.53 | 2.24 | 1.88 | 1.67”
    • Also stated in: § CONCLUSION · plain
      “O | (%) | 24.67 | 22.84 | 21.84 | 19.77 | 17.16 | 16.63 | 15.38 | 13.48”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Pyrolysis temperature is negatively correlated with the N content of STL biochar; N content decreased from 2.29 to 0.78% as temperature increased from 300 to 600 C.

    “The pyrolysis temperature was positively correlated to the ash content, pH, electrical conductivity, specific surface area (S BET ), pore volume (PV) and C content, and negatively with the total yield, O, H and N content, and the O/C and H/C atomic ratios.”
    • Also stated in: § Characteristics of STL biochar · plain
      “The average C content increased from 64.26 to 81.44%, while that of H, O and N respectively decreased from 3.71 to 1.78%, 23.76 to 14.43% and 2.29 to 0.78% as the pyrolysis temperature was increased from 300 to 600 C.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Pyrolysis temperature had a statistically significant effect on the yield, ash content, pH, EC, and CEC of STL biochar.

    “Temperature | | 787.344** | 399.224** | 531.125** | 118.023** | 457.141**”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    STL biochar with pH above 7.3 had more than 10% ash content, while samples with less than 7% ash content were acidic (pH < 7).

    “The STL biochar with pH above 7.3 had more than 10% ash content, while samples with less than 7% ash content were acidic (pH < 7).”
    Quote in the paperNot a substantial claim

  • The quote only partly states this claim.

    Findingown data

    The pseudo-second-order model described Cd(II) adsorption kinetics better than the pseudo-first-order model for the tested STL biochars, as indicated by higher R2 values.

    “1 h | 300 C | 26.376 | 0.997 | 0.876 | 28.207 | 0.053 | 0.988 | 27.97”
    Quote in the paperSubstantial claim

  • The quote only partly states this claim.

    Findingown data

    The Langmuir model fitted Cd(II) adsorption isotherms better than the Freundlich model for the tested STL biochars, as indicated by higher R2 values.

    “1 h | 300 C | 48.279 | 0.017 | 0.994 | 4.592 | 0.431 | 0.974”
    Quote in the paperSubstantial claim

  • May combine two claims. The quote only partly states this claim.

    Findingown data

    For STL biochar produced at any given pyrolysis temperature, increasing the pyrolysis duration from 1 h to 2 h increased the carbon content and C/N ratio and decreased the H, O, N, O/C, and H/C ratios.

    “C | (%) | 62.55 | 65.96 | 69.68 | 70.82 | 72.47 | 74.15 | 80.70 | 82.18”
    • Also stated in: § CONCLUSION · plain
      “H | (%) | 3.86 | 3.55 | 3.23 | 3.06 | 2.53 | 2.24 | 1.88 | 1.67”
    • Also stated in: § CONCLUSION · plain
      “O | (%) | 24.67 | 22.84 | 21.84 | 19.77 | 17.16 | 16.63 | 15.38 | 13.48”
    Quote in the paperSubstantial claim

  • The quote only partly states this claim.

    Findingown data

    The experimental Cd(II) adsorption capacity (qe,exp) of STL biochar increased with pyrolysis temperature and duration.

    “1 h | 300 C | 26.376 | 0.997 | 0.876 | 28.207 | 0.053 | 0.988 | 27.97”
    Quote in the paperSubstantial claim

  • The quote only partly states this claim.

    Findingown data

    The Langmuir maximum adsorption capacity (QL) for Cd(II) on STL biochar increased with pyrolysis temperature and duration.

    “1 h | 300 C | 48.279 | 0.017 | 0.994 | 4.592 | 0.431 | 0.974”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    The STL biochar was well carbonized and had sparse oxygen-containing functional groups on the surface.

    “Taken together, the STL biochar was well carbonized and had sparse oxygen-containing functional groups on the surface.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Pyrolysis at higher temperatures increases the exposed surface area as well as the number of adsorption sites on biochar for heavy metal ions.

    “Taken together, pyrolysis at higher temperatures increases the exposed surface area as well as the number of adsorption sites on biochar for heavy metal ions.”
    Quote in the paperSubstantial claim
33 of 33

  • The paper relies on this without support.

    The physiochemical properties of STL biochar that affect its ability to adsorb Cd(II) are still not well understood.

    “However, the physiochemical properties of STL biochar that affect its ability to adsorb Cd(II) are still not well understood.”
1 of 1

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Kinetic time and rate constants use incompatible time units

    Minor

    The kinetic equations use t measured in hours, but both rate constants are specified per minute. Without a conversion, their products in the stated equations have inconsistent units.

  • Reported O/C range excludes a table value

    Minor

    The stated minimum O/C ratio is 0.19, whereas Table 2 gives 0.16 for biochar produced at 600 C for 2 h.

2 of 2

Cites

Flagged first, then by citations

Cited by

Sorted by citations

Related

Authors
Yang, Z., Liu, X., Zhang, M., Liu, L., Xu, X., Xian, J., & Cheng, Z.
Affiliations
  • Sichuan Agricultural University (CN)
  • College of Environment, Sichuan Agricultural University, Chengdu 61130, China
Corresponding author
Yang, Zhanbiao
ORCID
Venue
Water Science and Technology
Publisher
IWA Publishing
Published
2020-06-15
Volume
81
Issue
12
Pages
2533-2544
ISSN
  • 0273-1223 (ISSN-L)
  • 1996-9732
DOI
10.2166/wst.2020.309
OpenAlex
W3039776681
Cited by
29
References
54
Citations by year
2026: 7 · 2025: 5 · 2024: 7 · 2023: 3 · 2022: 5 · 2021: 2
FWCI
0.77
Type
journal article
Language
en
Open access
Locations
  • Water Science & Technology (publishedVersion)
  • PubMed (publishedVersion)
Funders
  • National Natural Science Foundation of China (Grant No. 21507095)
  • Sichuan Provincial Youth Science and Technology Fund (Grant No. 2017JQ0035)
  • Sichuan Province Project Education Fund (Grant No. 16ZA0036)
Topics
  • Physical Sciences › Environmental Science › Water Science and Technology › Adsorption and biosorption for pollutant removal
  • Physical Sciences › Engineering › Biomedical Engineering › Thermochemical Biomass Conversion Processes
  • Physical Sciences › Engineering › Biomedical Engineering › Environmental remediation with nanomaterials
Keywords
spent tea leaves, biochar, pyrolysis temperature, pyrolysis duration, cadmium adsorption, heavy metal removal, physicochemical properties, surface porosity, oxygen-containing functional groups, pseudo-second-order kinetics, Langmuir isotherm, low-cost adsorbent, wastewater treatment
MeSH terms
Pyrolysis, Adsorption, Cadmium, Charcoal, Tea, Temperature, Plant Leaves

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-11.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-11.

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

What counts as a claim ›How we measure confidence ›How we check this ›

Are you an author, or do you see a problem with this page? Request a review