Hai Nguyen Tran

Effect of pyrolysis temperatures and times on the adsorption of cadmium onto orange peel derived biochar

The mechanism and capacity of adsorption of cadmium (Cd) on orange peel (OP)-derived biochar at various pyrolysis temperatures (400, 500, 600, 700 and 800°C) and heating times (2 and 6 h) were investigated. Biochar was characterized using proximate analysis, point of zero charge (PZC) analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. Equilibrium and kinetic experiments of Cd adsorption on biochar were performed. The results indicated that the pH value at PZC of biochar approached 9.5. Equilibrium can be reached rapidly (within 1 min) in kinetic experiments and a removal rate of 80.6–96.9% can be generated. The results fitted the pseudo-second-order model closely. The adsorption capacity was estimated using the Langmuir model. The adsorption capacity of Cd on biochar was independent of the pyrolysis temperature and heating time (p>0.01). The maximum adsorption capacity of Cd was 114.69 (mg g−1). The adsorption of Cd on biochar was regarded as chemisorption. The primary adsorption mechanisms were regarded as Cπ–cation interactions and surface precipitation. Cadmium can react with calcite to form the precipitation of (Ca,Cd)CO3 on the surface of biochar. The OP-derived biochar can be considered a favourable alternative and a new green adsorbent for removing Cd2+ ions from an aqueous solution.

Activated carbons from golden shower upon different chemical activation methods: Synthesis and characterizations

Activated carbons (ACs) were synthesized from golden shower (GS) through chemical activation. Two synthesis processes were used: one-stage and two-stage processes. In the one-stage process, GS that was impregnated with K2CO3 was directly pyrolyzed (GSAC), and the two-stage process consisted of (1) pyrolytic or hydrolytic carbonization to produce biochar or hydrochar and (2) subsequent chemical activation was defined as GSBAC and GSHAC, respectively. The activated carbon’s characteristics—thermal stability and textural, physicochemical, structural, and crystal properties—were thoroughly investigated. Results demonstrated that the characteristics of activated carbons strongly depend on the method used for their synthesis. The Brunauer–Emmett–Teller surface area followed the order GSAC (1413 m2/g) > GSHAC (1238 m2/g) > GSBAC (812 m2/g). The existence of acidic groups was determined through Fourier transform infrared spectroscopy and Boehm titration. The excellent adsorptive capacities of the activated carbons were confirmed from the iodine number (1568–2695 mg/g) and methylene number (143–233 mg/g).

Insight into adsorption mechanism of cationic dye onto agricultural residues-derived hydrochars: Negligible role of π-π interaction

Hydrochars derived from golden shower pod (GSH), coconut shell (CCH), and orange peel (OPH) were synthesized and applied to remove methylene green (MG5). The results indicated that the hydrochars possessed low specific surface areas (6.65-14.7m2/g), but abundant oxygen functionalities (1.69-2.12mmol/g). The hydrochars exhibited cellular and spherical morphologies. Adsorption was strongly dependent on the solution pH (2-10) and ionic strength (0-0.5M NaCl). Equilibrium can be quickly established in the kinetic study (60-120 min). The maximum Langmuir adsorption capacities at 30 °C followed the order GSH (59.6mg/g)>CCH (32.7mg/g)>OPH (15.6mg/g)> commercial glucose-prepared hydrochar (12.6mg/g). The dye adsorption efficiency was determined by the concentrations of oxygen-containing functionalities on the hydrochar surface. The adsorption process occurred spontaneously (− ΔGo) and exothermically (−ΔHo). Desorption studies confirmed the reversible adsorption process. Oxygenation of the hydrochar surface through a hydrothermal process with acrylic acid contributed to increasing MG5 adsorption and identifying the negligible role of π-π interaction to the adsorption process. The analysis of Fourier transform infrared spectrometry demonstrated that the aromatic C=C peak did not significantly decrease in intensity or shift toward higher/lower wavenumbers after adsorption, which further confirms the insignificant contribution of π-π interaction. Electrostatic attraction played a major role in adsorption mechanisms, while minor contributions were accounted for hydrogen bonding and n-π interactions. The primary adsorption mechanisms of MG5 onto hydrochar were similar to biosorbent, but dissimilar to biochar and activated carbon (i.e., π-π interaction and pore filling).

Activated carbon derived from spherical hydrochar functionalized with triethylenetetramine: synthesis, characterizations, and adsorption application

Abstract This study investigated the adsorption capacities of various contaminants on glucose-derived hydrochar (GH) and glucose-activated carbon (GAC) functionalized with triethylenetetramine (TETA). The two-stage synthesis process consisted of (1) hydrothermal carbonization using various TETA concentrations (1%–5%) to create TETA-functionalized GHs, and (2) chemical activation with NaOH to produce TETA-GACs. The basic properties of the adsorbents were examined using Brunauer-Emmett-Teller (BET) surface area analysis, Fourier transform infrared (FTIR) spectrometry, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy. The adsorption characteristics of the GH and GAC samples toward two heavy metal ions (Pb2+ and Cu2+), phenol, methylene green (MG5), and acid red 1 (AR1) were also examined. The results indicated that GAC1% and GH1% exhibited excellent adsorption capacities. Specifically, the maximum adsorption capacities of GAC1% and GH1% reached 370 mg/g and 128 mg/g for Pb2+, 208 mg/g and 84 mg/g for Cu2+, 196 mg/g and 137 mg/g for phenol, 175 mg/g and 67 mg/g for MG5, and 156 mg/g and 21 mg/g for AR1, respectively. In conclusion, amine functionalization on the surface of GHs and GACs efficiently enhances the removal capacities of various contaminants in water.

Insight into the adsorption mechanism of cationic dye onto biosorbents derived from agricultural wastes

ABSTRACT This study investigated the phenomenon and mechanism of adsorption of methylene green 5 (MG5) on three pristine biosorbents: golden shower pod (GS), coconut shell (CC), and orange peel (OP). The results showed that the biosorbents possessed low specific surface areas, but abundant functional groups. Adsorption was strongly affected by the solution’s pH and ionic strength. As revealed in the kinetic study, equilibrium was rapidly established, requiring low activation energies; a removal rate of 30%–87% was achieved within 1 min. The maximum Langmuir adsorption capacities at 30°C exhibited the following order: GS (106 mg/g) > OP (92 mg/g) > CC (59 mg/g). Thermodynamic experiments suggested that the adsorption occurred spontaneously (−ΔG°) and exothermically (−ΔH°). The primary adsorption mechanisms involved electrostatic attraction, hydrogen bonding formations, and n-π interaction. Thermogravimetric analysis (TGA) revealed that three biopolymer components (i.e., hemicellulose, cellulose, and lignin) played controlling roles in the adsorption process. Thus, these three agricultural residues can be considered potential low-cost adsorbents for efficient dye adsorption applications.

Saccharide-derived microporous spherical biochar prepared from hydrothermal carbonization and different pyrolysis temperatures: synthesis, characterization, and application in water treatment

ABSTRACT Three saccharides (glucose, sucrose, and xylose) were used as pure precursors for synthesizing spherical biochars (GB, SB, and XB), respectively. The two-stage synthesis process comprised: (1) the hydrothermal carbonization of saccharides to produce spherical hydrochar’ and (2) pyrolysis of the hydrochar at different temperatures from 300°C to 1200°C. The results demonstrated that the pyrolysis temperatures insignificantly affected the spherical morphology and surface chemistry of biochar. The biochar’ isoelectric point ranged from 2.64 to 3.90 (abundant oxygen-containing functionalities). The Brunauer–Emmett–Teller (BET)-specific surface areas (SBET) and total pore volumes (Vtotal) of biochar increased with the increasing pyrolysis temperatures. The highest SBET and Vtotal were obtained at a pyrolysis temperature of 900°C for GB (775 m2/g and 0.392 cm3/g), 500°C for SB (410 m2/g and 0.212 cm3/g), and 600°C for XB (426 m2/g and 0.225 cm3/g), respectively. The spherical biochar was a microporous material with approximately 71–98% micropore volume. X-ray diffraction results indicated that the biochar’ structure was predominantly amorphous. The spherical biochar possessed the graphite structure when the pyrolysis temperature was higher than 600°C. The adsorption capacity of GB depended strongly on the pyrolysis temperature. The maximum Langmuir adsorption capacities () of 900GB exhibited the following selective order: phenol (2.332 mmol/g) > Pb2+ (1.052 mmol/g) > Cu2+ (0.825 mmol/g) > methylene green 5 (0.426 mmol/g) > acid red 1 (0.076 mmol/g). This study provides a simple method to prepare spherical biochar – a new and potential adsorbent for adsorbing heavy metals and aromatic contaminants. GRAPHICAL ABSTRACT

Highly efficient removal of hazardous aromatic pollutants by micro-nano spherical carbons synthesized from different chemical activation methods: a comparison study

ABSTRACT Glucose-derived micro-nano spherical activated carbon (GAC) was synthesized through two-stage and three-stage chemical activation processes in different impregnation ratios (K2CO3: precursor). GAC was characterized by nitrogen adsorption/desorption isotherm, point of zero charge, scanning electron microscope, and Fourier transform infrared. The prepared spherical GAC and commercial non-spherical AC were applied to remove a cationic dye (methylene green 5; MG5), an anionic dye (acid red 1; AR1), and phenol. The batch adsorption experiments were conducted to analyse the effects of different operation conditions (i.e. solution pH, contact time, initial adsorbate concentration, temperature, and desorbing agent) on the adsorption process. The adsorption equilibrium was rapidly reached in kinetic experiments with a removal rate of 47–83% (within 1 min). The three-stage process-synthesized GAC exhibited the highest adsorption capacity, with the maximum adsorption capacity reaching at 1365 mg/g for MG5, 562 mg/g for AR1, and 322 mg/g for phenol adsorption. The process of MG5 and AR1 adsorption was endothermic (+ΔH°), while phenol adsorption was exothermic (–ΔH°). The primary adsorption mechanism was pore filling and π-π interactions. The pore of spherical GAC might be easily enlarged than that of non-spherical AC when the temperature of solution increased. Therefore, the spherical activated carbon can server as a green promising and renewable adsorbent for efficiently remove hazardous aromatic pollutants from aquatic environment. GRAPHICAL ABSTRACT

Characteristics and mechanisms of cadmium adsorption onto biogenic aragonite shells-derived biosorbent: Batch and column studies

Calcium carbonate (CaCO3)-enriched biomaterial derived from freshwater mussel shells (FMS) was used as a non-porous biosorbent to explore the characteristics and mechanisms of cadmium adsorption in aqueous solution. The adsorption mechanism was proposed by comparing the FMS properties before and after adsorption alongside various adsorption studies. The FMS biosorbent was characterized using nitrogen adsorption/desorption isotherm, X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy, Fourier-transform infrared spectroscopy, and point of zero charge. The results of batch experiments indicated that FMS possessed an excellent affinity to Cd(II) ions within solutions pH higher than 4.0. An increase in ionic strength resulted in a significant decrease in the amount of Cd(II) adsorbed onto FMS. Kinetic study demonstrated that the adsorption process quickly reached equilibrium at approximately 60 min. The FMS biosorbent exhibited the Langmuir maximum adsorption capacity as follows: 18.2 mg/g at 10 °C < 26.0 mg/g at 30 °C < 28.6 mg/g at 50 °C. The Cd(II) adsorption process was irreversible, spontaneous (-ΔG°), endothermic (+ΔH°), and more random (+ΔS°). Selective order (mmol/g) of metal cations followed as Pb2+ > Cd2+ > Cu2+ > Cr3+ > Zn2+. For column experiments, the highest Thomas adsorption capacity (7.86 mg/g) was achieved at a flow rate (9 mL/min), initial Cd(II) concentration (10 mg/L), and bed height (5 cm). The Cd(II) removal by FMS was regarded as non-activated chemisorption that occurred very rapidly (even at a low temperature) with a low magnitude of activation energy. Primary adsorption mechanism was surface precipitation. Cadmium precipitated in the primary (Cd,Ca)CO3 form with a calcite-type structure on the FMS surface. A crust of rhombohedral crystals on the substrate was observed by SEM. Freshwater mussel shells have the potential as a renewable adsorbent to remove cadmium from water.