Adsorption of lead ions and methylene blue on acrylate-modified hydrochars

Effect of oxygen-containing functional group contents on sorption of lead ions by acrylate-functionalized hydrochar

The surface functional groups of hydrochar are crucial to its surface properties, and their contents are strongly positively correlated with the adsorption performance. In this study, acrylate-functionalized hydrochar (AHC) with varying contents of O-containing functional groups (OFGs) was synthesized via hydrothermal carbonization (HTC) of bamboo, acrylic acid and an initiator, and then deprotonated with NaOH. The AHCs were analyzed by various characterization techniques. During HTC, the higher amount of acrylic acid added led to higher carbon, oxygen and carboxyl contents, and to the larger specific surface area and pore volume of AHC. The adsorption kinetics, isotherms, thermodynamic, ionic strength and pH effects of Pb(II) on AHC were studied. Adsorption isotherms and kinetics obeyed Langmuir and pseudo-second-order models, respectively, indicating adsorption is monolayer chemical process. The adsorptive ability was well linearly related to the OFG contents of AHC. When acrylic acid was added to 25 mL during HTC, the adsorbing ability of AHC over Pb(II) reached 193.90 mg g-1. Hence, direct HTC of acrylic acid, biomass and an initiator can prepare hydrochar with controllable OFG contents, which is a prospective adsorbent for treating metal cations.

Adsorption performance of mineral-carbon adsorbents derived from coal gasification fine ash: Prepared via low-temperature alkali fusion method

To address the solid waste challenges associated with coal gasification fine ash, this study conducted a low-temperature alkali fusion de-ashing treatment to transform coal gasification fine ash into mineral-carbon adsorbent. The preparation process was simplified without grinding, carbonization and high-temperature (500-800 °C) activation treatment. The results demonstrate a positive linear correlation between the ash removal rate of the samples (measured during the preparation process, i.e., low-temperature alkaline fusion treatment of coal gasification fine ash) and their maximum equilibrium adsorption capacity for methylene blue. For the samples with an ash removal rate of 95.71 %, which exhibit a maximum adsorption capacity of 161.36 mg/g for methylene blue. The adsorption behavior of methylene blue on mineral-carbon adsorbent was a monolayer adsorption on the surface of homogeneous medium, involving both physical and chemical adsorption. The main adsorb rate-controlling steps for the samples with ash removal rates of 27.91-59.33 % and 95.71 % were the intra particle diffusion process and the liquid film diffusion process, respectively. The adsorption mechanism of methylene blue on the surface of mineral-carbon adsorbent involved electrostatic attraction and hydrogen bonding. The aforementioned results demonstrated the potential of coal gasification fine ash as an adsorbent material, providing new options for promoting the resource utilization and high-value applications of coal gasification fine ash.

A review: Hydrochar as potential adsorbents for wastewater treatment and CO2 adsorption

To valorize the biomass and organic waste, hydrothermal carbonization (HTC) stands out as a highly efficient and promising pathway given its intrinsic advantages over other thermochemical processes. Hydrochar, as the main product obtained from HTC, is widely applied as a fuel source and soil conditioner. Aside from these applications, hydrochar can be either directly used or modified as bio-adsorbents for environmental remediation. This potential arises from its tunable surface chemistry and its suitability to act as a precursor for activated or engineered carbon. In view of the importance of this topic, this review offers a thorough examination of the research progress for using hydrochar and its modified forms to remove organic dyes (cationic and anionic dyes), heavy metals, herbicides/pesticides, pharmaceuticals, and CO2. The review also sheds light on the fundamental chemistry involved in HTC of biomass and the major analytical techniques applied for understanding surface chemistry of hydrochar and modified hydrochar. The knowledge gaps and potential hurdles are identified to highlight the challenges and prospects of this research field with a summary of the key findings from this review. Overall, this article provides valuable insights and directives and pinpoints the areas meriting further investigation in the application potential of hydrochar in wastewater management and CO2 capture.

Effects of cation types in persulfate on physicochemical and adsorptive properties of biochar prepared from persulfate-pretreated bamboo

The adsorption behaviors of biochar are largely impacted by biomassfeedstock. In this study, two biochars were prepared from torrefaction of ammonium persulfate- and potassium persulfate-pretreated bamboo and then activated by cold alkali, which are named as ASBC and KSBC, respectively. The two biochars were characterized by different instruments, and their adsorption properties over cationic methylene blue (MB) were compared. The type of persulfates little affected the specific surface areas, but significantly impacted O (29.54 % vs. 35.113 %) and N (12.13 % vs. 3.74 %) contents, functional groups, and zeta potentials of biochars. MB adsorption onto ASBC/KSBC is a single-layer chemical endothermic process and ASBC/KSBC exhibit high adsorption capacity over MB (475/881 mg·g-1) at 303 K. Obviously, the sorption capacity of MB onto KSBC much surpasses that of MB onto ASBC. These results indicate biomass pre-treatment is a cheap and convenient method to prepare biochars with unique physicochemical and adsorptive properties.

Removal of methylene blue by acrylic polymer adsorbents loaded with magnetic iron manganese oxides: Synthesis, characterization, and adsorption mechanisms

Dyes pose significant risks for aquatic environments and biological health in general owing to their non-biodegradable nature, carcinogenicity, and toxicity. The effective treatment of dye wastewater has become an important research topic. In this study, acrylic polymers (AP) loaded with magnetic iron manganese oxides (MIMO) (AP/MIMO) were prepared and used for the first time for the adsorption of methylene blue (MB). Carbon in AP/MIMO exists predominantly in the C-H and C-C forms, with its content reaching 50.7%. Oxygen and nitrogen in AP/MIMO exist mainly in the -CO- and -N-C forms, with contents of up to 41.5% and 73.3%, respectively. MB removal by AP/MIMO was consistent with the pseudo-second-order kinetic model (R2 = 0.99), equilibrium was achieved within 20 min, and the highest MB capacity of 2611.23 mg g-1 was predicted by the Langmuir isotherm model (R2 = 0.91-0.94). AP/MIMO exhibited excellent MB adsorption performance in the pH range of 4-10, with a removal efficiency higher than 99.0% (MB = 100 mL 1000 mg L-1; AP/MIMO = 50 mg). Thermodynamic indicators, such as positive entropy (ΔS0; 98.30 J⋅mol-1⋅K-1), negative Gibbs free energy (ΔG0; -29.40, -28.50, and -27.50 KJ⋅mol-1), and positive enthalpy (ΔH0; 2.30 KJ⋅mol-1), demonstrated that MB removal by AP/MIMO was autonomous, favorable, and endothermic. In addition, the integration of experimental results and theoretical calculations verified that electrostatic interactions were the primary mechanism for MB adsorption at carboxyl sites on AP/MIMO. The total interaction energy between AP and MB was -310.43 kJ⋅mol-1, and the electrostatic effect had a decisive contribution to the MB adsorption, with a value of up to -341.06 kJ⋅mol-1. AP and MB were most likely bound by -COO and S atoms. Overall, AP/MIMO exhibits high adsorption capacity and shows potential as a high-performance magnetic polymer for MB removal.

Preparation of amphoteric double network hydrogels based on low methoxy pectin: Adsorption kinetics and removal of anionic and cationic dyes

The objective of this research was to devise a functional hydrogel was synthesized using pectin (PE), acrylic acid (AA), dimethyldiallyl ammonium chloride (DC), and polyvinyl alcohol (PVA), designed to adsorb both cationic and anionic dyes concurrently. The low methoxy pectin formed double network hydrogel through chemical and physical crosslinking with AA and PVA respectively. DC is combined into the hydrogel system through copolymerization reaction. Analysis of hydrogel's physicochemical properties was conducted using techniques such as infrared spectroscopy, texture analysis, thermogravimetry, and scanning electron microscopy. Dyes adsorption studies showed that the LP/AA/DC/PVA-2 hydrogel, prepared at the molar ratio of AA to DC of 1:2, exhibited higher adsorption efficiency for methylene blue (MB) and Congo red (CR). Kinetics and isotherms studies indicated that the adsorption behavior conformed to the pseudo-second-order kinetic model and Langmuir isotherm model. By the Langmuir isotherm fitting, the maximum adsorption capacities of MB and CR by LP/AA/DC/PVA-2 were recorded to be 222.65 mg/g and 316.46 mg/g, respectively. The adsorption mechanism is dominated by the hydrogen bonding and electrostatic interactions. Further, the adsorption and desorption experiments demonstrated that LP/AA/DC/PVA-2 hydrogel have excellent reusability.

Trithiocyanurate-functionalized hydrochar for effectively removing methylene blue and Pb (II) cationic pollutants

Functionalization can change the physicochemical properties of hydrochar and improve its ability to adsorb pollutants. Herein, a trithiocyanurate-functionalized hydrochar (TTHC) was obtained from acylation of chloroacetyl chloride and hydrochar and modification with trithiocyanuric acid in alkaline conditions. TTHC can efficiently remove cationic methylene blue (MB) and Pb(II) from wastewater. The removal can be expressed with pseudo-second-order kinetic and Langmuir models. The MB and Pb(II) removed uptakes by TTHC at 298 K exceeded 909.9 and 182.8 mg g-1 respectively, and the removal rates reached 90% and 98% within 120 min respectively. Characterizations show TTHC is functionalized with trithiocyanurate, and rich in thiolate and aromaticity, and tends to adsorb MB/Pb(II) via multiple adsorption mechanisms. After five sorption-desorption regeneration cycles, TTHC maintained 80% and 99% adsorption capacities for MB and Pb(II) respectively. Therefore, TTHC is a promising efficient sorbent for removing MB and Pb(II) from effluents.

A comparative study of methylene blue adsorption and removal mechanisms by calcium carbonate from different sources

Efficient removal of organic dye pollution from contaminated water is a concern in the absorbent applications. In this study, a green biogenic calcium carbonate (BCC) absorbent was fabricated using Bacillus licheniformis for the removal of methylene blue (MB) from water. This was found to have superior adsorption capacity compared with abiotic calcium carbonate (ACC) and operate within a broad pH range from 3 to 9. MB adsorption on BCC was physical and exothermic. The hydrophobic features, rough nanoporous microstructure, and organic-inorganic mesoporous structure of the BCC may all be responsible for its favorable adsorption mass transfer. The adsorption energy of BCC had a more negative value than that of ACC, indicating a stronger MB interaction with BCC with a lower energy barrier. Hydrogen bonding and electrostatic attraction were involved in the adsorption process. Overall, the findings established a theoretical foundation for the application of BCC in remediation of MB-contaminated water.

Enhanced removal of Cr(VI) by polyethyleneimine-modified bamboo hydrochar

Hydrochar is an environmentally friendly and cheap adsorbent, but its adsorption amounts for anions is very limited. The functionalized hydrochar can overcome this shortcoming. Herein, polyethyleneimine-modified hydrochar (PEI-HC) was synthesized from hydrothermal carbonization (HTC) of methyl acrylate and bamboo after addition of initiator ammonium persulfate, and then modified by polyethyleneimine (PEI), which was used to treat Cr(VI). PEI-HC was tested by XANES, EXAFS, SEM-EDS, XPS, FTIR, N2 sorption isotherms, zeta potential, and elemental analyses. The characterizations showed that PEI was successfully grafted onto hydrochar, and the PEI-HC was rich in N and O functional groups, which presented high Cr(VI) sorption ability (528.41 mg·g-1 at pH 2). The bath experiments found the pseudo-second-order kinetic and Freundlich equations can well describe the adsorption kinetics and isotherm of the Cr(VI) adsorption onto PEI-HC, respectively. Electrostatic interaction, reduction, complexation, and H-bonding are the main removal mechanisms as supported by XANES, EXAFS, XPS, and FTIR. This study provides a strategy of combining HTC and free radical graft polymerization to convert agricultural and forestry wastes into functionalized hydrochar, showing highly efficient removal of Cr(VI).