Preparation of Edible Colorant Lake Using Calcium Carbonate and β-Carotene: Structural Characterization and Formation Mechanism Study

This study prepared a novel β-carotene colorant lake using calcium carbonate (CaCO3) and investigated the lake formation process and its basic characteristics. Kinetic adsorption analysis confirmed that medium pH (9.3) and medium temperature (40 °C) were more suitable for lake preparation, while desorption occurred, possibly due to crystalline transformation of CaCO3. The isothermal analysis and model fitting results suggested that the β-carotene and CaCO3 particles combined via a monolayer adsorption process driven by physical force. Electrostatic attraction likely participated in the process due to the net negative surface charges of β-carotene dispersion and positively charged groups on the CaCO3 particle surfaces. Ethanol, ultrasonic treatment, and drying method significantly influenced the immobilization efficiency (IE) of β-carotene in the lake and light stability of the lake, without affecting its crystal form. The thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) curves confirmed absorption of β-carotene onto CaCO3. Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses indicated no obvious chemical bonds between β-carotene and CaCO3. Energy-dispersive spectroscopy (EDS) confirmed the presence of β-carotene on surfaces but not in the interior of the CaCO3 particles. The adsorption of β-carotene by calcium carbonate was further confirmed to be a physical adsorption on surface.

[Effects of maltodextrin on water adsorption and thermodynamic properties of Codonopsis Radix spray-dried powder]

This study aims to reveal the effects of maltodextrin(MD) on the water adsorption and thermodynamic properties of Codonopsis Radix(DS) spray-dried powder by determining the moisture and energy changes of the powder in the process of moisture absorption. The static weighing method was used to obtain the isothermal water adsorption data of the spray-dried powder in 6 saturated salt solutions(KAc, MgCl_2·6H_2O, K_2CO_3, NaBr, NaCl, and KCl) at 3 temperatures(25, 35, and 45 ℃). Six models were used for fitting of the water adsorption process, and the most suitable model was selected based on the model performance. Furthermore, the corresponding net equivalent adsorption heat and differential entropy were calculated, and the adsorption entropy change was integrated. The linear relationship between net equivalent adsorption heat and differential entropy was drawn based on the entropy-enthalpy complementarity theory. The results showed that the water adsorption properties of DS and DS-MD spray-dried powder followed the type Ⅲ isotherm and was well fitted by the GAB model. The monolayer water content M_0 decreased with the increase in temperature. At the same temperature, the M_0 of DS spray-dried powder decreased after the addition of MD. The net equivalent adsorption heat and differential entropy of DS and DS-MD spray-dried powder decreased with the increase in water content, which presented a linear relationship. The addition of MD decreased the water activity corresponding to the lowest integral adsorption entropy of the powder, and the system became more stable. The results indicated that the spray-dried powder became more stable after the addition of MD.

Removal of Fe2+ and Mn2+ from Polluted Groundwater by Insoluble Humic Acid/Tourmaline Composite Particles

Insoluble humic acid/tourmaline composite particles (IHA/TM) were prepared by combining inorganic tourmaline (TM) with the natural organic polymer humic acid (HA) and carbonizing them at 330 °C to study the removal characteristics and mechanism of Fe²⁺ and Mn²⁺. The results showed that the optimal ratio of TM to IHA is 2:3. When the temperature of the IHA/TM composite particles was 35 °C and the pH was 6, the adsorption of Fe²⁺ and Mn²⁺ by IHA/TM reached equilibrium at 240 min. The optimum dose of the adsorbent was 10 g/L, and the equilibrium adsorption capacities of Fe²⁺ and Mn²⁺ were 5.645 mg/g and 3.574 mg/g, respectively. The process of IHA/TM adsorption of Fe²⁺ and Mn²⁺ in water was spontaneous, endothermic and sustainable, and cooling was not conducive to adsorption. The pseudo-second order kinetic equation can well reflect the adsorption mechanism of IHA/TM on Fe²⁺ and Mn²⁺, and the Langmuir adsorption model better describes the isothermal adsorption behaviour. The material characterisation and adsorption experiments indicate that surface coordination and chemical precipitation are the main mechanisms of Fe²⁺ and Mn²⁺ removal by IHA/TM.

Enhanced removal of Congo red dye from aqueous solution by surface modified activated carbon with bacteria

AIMS

The adsorption behaviour and mechanisms of the surface modified activated carbon with bacteria was evaluated.

METHODS AND RESULTS

16S rRNA was employed to identify the hydrocarbon-degrading bacteria. The bacteria was characterized by TEM and electron microscope. The surface modified activated carbon with bacteria was characterized by SEM. The adsorption behaviour was tested by static adsorption and dynamic adsorption.

CONCLUSION

The adsorption efficiency of the modified activated carbon was high when pH was weak acidic, and the adsorption capacity increased with the increase of temperature ranging from 20 to 35°C. The adsorption capacity peaked at 234·6 mg g^-1 at 25°C, which was sixfold higher than that of activated carbon. The pseudo-first-order kinetic can more accurately assess Congo red adsorption on the two adsorbents. The adsorption of Congo red by bacteria surface modified activated carbon fitted well with the Langmuir's model. The adsorption process was endothermic, and the biological floccules were formed during the adsorption. The physical adsorption is the main driving force.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results indicate that the bacteria surface-modified activated carbon can be used effectively as an adsorbent to eliminate Congo red from aqueous solutions.

[Effect of Biochar Structure on Adsorption Characteristics of Ammonia Nitrogen]

Ammonia inhibition is a common phenomenon in biogas engineering which is rich in organic nitrogen substrate. Ammonia nitrogen in anaerobic digestate slurry can be fixed by biochar adsorption. Biochar is prepared from corn stalks and rice husks as raw materials at different temperatures (350℃, 450℃, and 550℃). The purpose is to explore the correlation between the physical and chemical structure of biochar and the adsorption characteristics of ammonia nitrogen. The structure and physicochemical properties of biochar were analyzed by elemental analysis, FTIR, BET, etc., and batch adsorption experiments were conducted to investigate the effect of biochar with different physicochemical properties on adsorption characteristics of ammonia nitrogen. The results indicated that the carbon and ash content in biochar increases with an increase in pyrolysis temperature; the NH₄⁺-N adsorption of the corn stalk biochar prepared at 450℃ (CS450) and the rice husk biochar prepared at 550℃ (RH550) follows the quasi-secondary-and quasi-first-order kinetic models. The Freundlich adsorption model can better describe the isothermal adsorption process of ammonia nitrogen in CS450 and RH550 biochar. The adsorption capacity of corn straw carbon correlated strongly with its surface functional groups. The most significant correlation with the adsorption capacity of rice husk carbon is the specific surface area of biochar, followed by surface functional groups, and finally ash content. Among them, RH550 had the best adsorption performance, and the maximum adsorption capacity was 12.16 mg·g^-1.

[Preparation of MgO Modified Lotus Shell Biochar and Its Phosphorus Adsorption Characteristics]

To study the potential application characteristics of biochar as a phosphate adsorbent, nano-MgO-biochar was prepared by rapid pyrolysis of a mixture of MgO and lotus shells. The physicochemical properties were characterized by XRD, BET, SEM, and TEM, and adsorption experiments were conducted. The results showed that MgO was mainly supported on the surface of carbon in the form of flakes and granules, which increased the adsorption active site, and the adsorption amount of MgO-biochar MBC3 was 14 times higher than that of biochar MBC1 without MgO. The adsorption capacity of MBC9, which was prepared by rapid pyrolysis under 10% CO₂ atmosphere, was further increased 16 times higher than that of MBC1. The adsorption kinetics followed a pseudo-second-order model, which indicated the adsorption of phosphate on MgO-biochar was dominated by chemical adsorption. According to the Langmuir equation, the maximum adsorption capacity of MBC3 and MBC9 could reach 283.26 mg·g^-1 and 297.96 mg·g^-1, respectively. MgO-biochar is a high-efficiency phosphate adsorbent, which can be used to control the eutrophication of water.

Effects of Surface Functional Groups on the Adhesion of SiO2 Nanospheres to Bio-Based Materials

The interactions between nanoparticles and materials must be considered when preparing functional materials. Although researchers have studied the interactions between nanoparticles and inorganic materials, little attention has been paid to those between nanoparticles and bio-based protein materials, like leather. In this study, organically modified silica nanospheres (SiO₂ nanospheres) loaded with rose fragrance were prepared using (3-aminopropyl) triethoxysilane (APTES), (3-mercaptopropyl) triethoxysilane (MPTES), or 3-(2, 3-epoxypropyloxy) propyl triethoxysilane (GPTES) using the sol-gel method. To study the interactions between the modified SiO₂ nanospheres and leather, a non-cross-linking adsorption experiment was conducted. According to the Dubinin–Radushkevich isotherm calculation, we found that the adsorption process of leather fiber and organically modified silica nanospheres is physical. The average adhesion energies of APTES-, MPTES-, and GPTES-modified SiO₂ nanospheres on the leather are 1.34016, 0.97289, and 2.09326 kJ/mol, respectively. The weight gain, adsorption capacity, and average adhesion energy show that the modified SiO₂ nanospheres can be adsorbed on leather in large quantities. The sensory evaluation confirmed that GPTES-modified SiO₂ nanospheres endowed the leather with an obvious rose aroma.

[Adsorption of Tetracycline on Simulated Suspended Particles in Water]

The mechanism of adsorption of a typical antibiotic (tetracycline, TC) on particles in the aquatic environment and the parameters affecting adsorption were investigated. Experiments were conducted to elucidate the effects of pH and various cation species with different concentrations. The results show that the adsorption of TC on particles is rapid during the first four hours in the mixing stage. The adsorption process becomes slow after the first four hours. The adsorption of TC on particles can be described well by a Langmuir equation. The maximum adsorption of TC on particles occurs at pH 4.5, however it is reduced by strongly acidic (pH<4) or alkaline (pH>9) conditions. Moreover, the adsorption process is also inhibited by various cations (e.g. Na⁺ and Ca²⁺) in the range of 0.0001-0.1 mol·L^-1 ionic concentrations. A special finding concerns Al³⁺ ions; at a low concentration of these ions (0-0.0001 mol·L^-1) the adsorption of TC on particles improves, whereas at increased concentrations the adsorption is weakened. In summary, an effective removal of the particles is critical to control TC pollution in natural waters because of the rapid adsorption of TC on particles.

[External Phosphorus Adsorption and Immobility with the Addition of Ignited Water Purification Sludge]

The cumulative adsorption of external phosphorus (P) by water purification sludge after ignition under different addition methods (mix and cover) was investigated along with the adsorption isotherm and the release of internal P after external P adsorption. The cumulative adsorption of external P was 11.496 mg (mix) and 11.042 mg (cover) and these values were higher than those in the control (7.219 mg). The maximum sorption capacity (S_max) increased under the mix and cover and the former (7.795 mg·g^-1) was higher than the latter (6.807 mg·g^-1). However, the zero equilibrium P concentration (EPC₀) in the mix was 0.83 mg·L^-1, higher that in the cover (0.64 mg·L^-1). The result suggests that the internal P was easily released in the mix method, compared to the cover method. Under anaerobic conditions, the release of the internal P was 0.93 mg in the mix, lower than that in the cover (1.49 mg) and in the control (7.76 mg). In addition, the specific release rate in the cover method was 0.00614 (mean), higher than that (0.00396) in the mix method. Noticeably, these data were lower than those in the control, indicating that the retention of P under the mix method was higher, compared to the cover and the control and it is challenging to evaluate the P retention with EPC₀.

[Adsorption Characteristics of Phosphorus Wastewater on the Synthetic Ferrihydrite]

The synthetic ferrihydrite, FerrorMox (FM), was used as adsorbent for removing phosphorus from wastewater. SEM, EDS, XRD, FTIR and Raman were used to characterize FM, and the results indicated that FM was amorphous 2 L ferrihydrite and was composed of Fe, O, Ca and Si, etc. Afterwards, FM was applied to adsorb phosphorus from wastewater, and the adsorption performance, influence factors and adsorption mechanism were investigated. The phosphorus removal rate reached 99.14% under the condition of adsorption time of 60 min, initial pH phosphate solution of 2, relative dosing quantity of 7 g·L^-1, reaction temperature of 25℃, initial concentration of 10 mg·L^-1, and solution volume of 50 mL. Adsorption isotherms were well fitted with the Langmuir isothermal adsorption model at different temperature with the correlation coefficient reaching above 0.95. The thermodynamic parameters showed that the phosphorus adsorption by FM was a spontaneous endothermic reaction. The phosphate removal kinetics well followed both pseudo-first-order model and pseudo-second-order model. About 99% of phosphate adsorbed on FM could be desorbed in 0.1 mol·L^-1 NaOH solution. Therefore, FM was a promising absorbent material for the removal of phosphate from waste water.