Synthesis of Mesoporous Silica Materials via Nonsurfactant Urea-Templated Sol-Gel Reactions

Mesoporous silica materials with pore diameters of 2 to 6 nm have been prepared using urea as a nonsurfactant template or pore-forming agent in HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate, followed by removing the urea molecules by extraction with methanol or water. Characterization results from nitrogen sorption isotherm, powder X-ray diffraction, and transmission electron microscopy indicate that the materials have large specific surface areas (e.g., 600 m²/g) and pore volumes (e.g., 0.8 cm³/g) as well as narrow pore size distributions. The mesoporosity is arisen from interconnecting wormlike channels and pores of regular diameters. As the urea concentration is increased, the nitrogen sorption isotherms of the silica matrices transform from the reversible type I to the type IV form with type H2 hysteresis, along with increases in the diameter and volume of the pores.     

Hydroxyethyl cellulose hydrogel modified with tannic acid as methylene blue adsorbent

This work developed an effective way to improve the methylene blue (MB) adsorption performance of cellulose-based hydrogel by modified with tannic acid (TA). HEC-co-p(AA-AM)/TA hydrogel was synthesized by grafting of acrylic acid (AA) and acrylamide (AM) onto hydroxyethyl cellulose (HEC), followed by modified with TA. Fourier transform infrared spectroscopy manifested that AA and AM were successfully grafted onto the hydrogel, and TA was immobilized in the hydrogel. Field emission scanning electron microscope demonstrated that the hydrogel after TA modification had a homogeneous pore structure. Brunauer-Emmett-Teller (BET) surface areas, total pore volume, and average pore diameters of the hydrogel are 11.821 m² g⁻¹, 0.0641 cm³ g⁻¹, and 2.538 nm, respectively. The high swelling ratio (1179.2 g g⁻¹ in deionized water) was in favor of the MB adsorption. The results of the adsorption experiments illustrated that HEC-co-p(AA/AM) hydrogel had excellent MB adsorption performance. As the pH increases, the electrostatic attraction is enhanced, and the adsorption capacity is improved. The adsorption process was more fit with pseudo-second-order kinetics, and the maximum adsorption capacity (3438.27 mg g⁻¹) was determined by Langmuir model. Thermodynamic studies suggested that the adsorption process is spontaneous, exothermic, and entropy reduction. X-ray photoelectron spectroscopy analysis confirmed that MB molecules were reacted with the oxygen atoms in hydroxyl and carboxyl groups by ion-exchange. High reusability demonstrated that the hydrogel could be a potential candidate for removal cationic dye from industrial effluents.     

Preparation of hierarchical magnesium silicate with excellent adsorption capacity

Magnesium silicate (MS) is a widely used adsorbent, and much work has been done to control the surface morphology of MS to improve its adsorption capacity. In this work, hierarchical MS was prepared by combining hydrothermal process with freeze drying technique for potential application in adsorption. Firstly, the MS hydrogel was prepared by hydrothermal process, followed by replacement of water in hydrogel by tert-butyl alcohol. Finally, the MS was obtained by freeze drying. The prepared MS exhibited a rough and porous hierarchical structure having BET specific surface area and total pore volume of 530?m²/g and 0.90?cm³/g, respectively. MS was further used for methylene blue (MB) adsorption in aqueous solution and the adsorption data exhibited good correlation with the Langmuir adsorption isotherm model. The maximum adsorption capacity for MB was found to be 526?mg/g, far higher than the conventional adsorbents that popularly reported in literature. In conclusion, this work provides a novel route to prepare adsorbents with high adsorption performance.     

高比表面磁性有序介孔炭的合成及对亚甲基蓝的吸附性能

具有高比表面积、大孔容的铁磁性有序介孔炭(Fe/OMCs)对含染料废水的处理提供了一种简单有效的方法。采用苯酚树脂作炭源,三嵌段共聚物F127为模板剂,正硅酸乙酯为硅前驱体,硝酸铁为磁源,通过软模路线合成了Fe/OMCs。利用X射线衍射仪(XRD),氮气吸附仪,透射电镜(TEM)和综合物性测试仪研究了硝酸铁加入量对Fe/OMCs的相态、孔结构参数和磁性的影响;并以亚甲基蓝(MB)为染料探针分子,研究了Fe/OMCs对MB的吸附行为。结果表明材料有序性、比表面和孔容随着硝酸铁加入量的增加而降低,而饱和磁化强度明显增强。Fe/OMCs对MB有快速吸附能力,其行为符合Sips吸附方程。     

Large scale fabrication of porous boron nitride microrods with tunable pore size for superior copper (II) ion adsorption

Herein, large scale fabrication of porous boron nitride (BN) microrods has been achieved via a facile process, which involves the synthesis of melamine diborate precursors and subsequent thermal treatment process. The fabrication can be scaled up to ultra-large scale which is limited by the furnace. The characterization results show that the as-obtained products are porous BN microrods with diameters in the range of ten to tens of micrometers and length of a few millimeters, respectively. The specific surface area and porosity of these porous BN microrods are tunable by adjusting the synthesis processes of precursors. A highest specific surface area of 653.66?m²/g is obtained for the sample of BN-4, corresponding to the differential pore volume of 0.289?cm³/(g?nm) and pore size of about 1.928?nm. Further measurement shows that the as-obtained porous BN microrods possess excellent copper ion adsorption property with a highest adsorption capacity of 365.4?mg/g. This adsorption capacity is superior to those of most copper ion adsorbents reported in recent literature. The high copper ion adsorption capacity combining with the unique properties of hexagonal BN makes them promising candidates for copper ions adsorption in practical wastewater treatment.     

Electron microscopy and nitrogen adsorption studies of film-type carbon replicas with large pore volume synthesized by using colloidal silica and SBA-15 as templates

Mesoporous carbons synthesized by the film-type replication of colloidal silica and SBA-15 templates are studied by electron microscopy and nitrogen adsorption. This synthesis strategy involves the formation of thin carbon film on the pore walls of these templates using resorcinol-crotonaldehyde polymer as carbon precursor. For the silica templates consisting of 20-80 nm colloids this synthesis affords carbons with extremely large pore volumes (5-9 cm³/g) and uniform spherical pores reproducing the size of the colloids used.     

EFFECT OF TEMPERATURE ON THE ADSORPTION OF METHYLENE BLUE DYE ONTO SULFURIC ACID–TREATED ORANGE PEEL

The present study explains the preparation and application of sulfuric acid–treated orange peel (STOP) as a new low-cost adsorbent in the removal of methylene blue (MB) dye from its aqueous solution. The effects of temperature on the operating parameters such as solution pH, adsorbent dose, initial MB dye concentration, and contact time were investigated for the removal of MB dye using STOP. The maximum adsorption of MB dye onto STOP took place in the following experimental conditions: pH of 8.0, adsorbent dose of 0.4 g, contact time of 45 min, and temperature of 30°C. The adsorption equilibrium data were tested by applying both the Langmuir and Freundlich isotherm models. It is observed that the Freundlich isotherm model fitted better than the Langmuir isotherm model, indicating multilayer adsorption, at all studied temperatures. The adsorption kinetic results showed that the pseudo-second-order model was more suitable to explain the adsorption of MB dye onto STOP. The adsorption mechanism results showed that the adsorption process was controlled by both the internal and external diffusion of MB dye molecules. The values of free energy change (ΔG ^o) and enthalpy change (ΔH ^o) indicated the spontaneous, feasible, and exothermic nature of the adsorption process. The maximum monolayer adsorption capacity of STOP was also compared with other low-cost adsorbents, and it was found that STOP was a better adsorbent for MB dye removal.     

Preparation and characterization of polyurethane foam/activated carbon composite adsorbents

A polyurethane foam (PU)/activated carbon (AC) composite was prepared by adding granular AC during the synthesis of PU foam, and subsequent carbonization. Nitrogen adsorption?Cdesorption isotherms and scanning electron microscopy were used to ascertain the pore structure and surface morphology of the samples. The prepared composite foams possess well-developed open cell structures. Under the conditions investigated, a higher carbonization temperature promoted development of porous structures. Thermogravimetric and derivative thermogravimetric analyses revealed the thermostability of the PU foam precursor/AC composites. The adsorption performance of the composites was evaluated using phenol, iodine and methylene blue (MB) as model compounds. A PU foam/AC composite with a maximum specific surface area of 655.0?m²/g, maximum iodine number of 525.2?mg/g, and maximum adsorption capacity of MB and phenol of 100 and 66.5?mg/g, respectively, was achieved.     

The efficient removal of organic pollutant over magnetic mesoporous polymer

Nanoporous polymers due to their abundant pores and organic frameworks are very suitable for the adsorption of organic pollutants in aqueous solution. However, the difficulty in separation and recovery limit their widely practical applications. Herein, polydivinylbenzene was first synthesized by solvothermal method, then magnetic Fe₃O₄ precursors were incorporated into the polymer framework to obtain magnetic polydivinylbenzene, designated as Fe₃O₄/PDVB. The as-prepared magnetic mesoporous polymer possessed rich porous structure, high specific area of 444.7 m²/g, pore size of 8.9 nm and pore volume of 0.82 cm³/g, which were fully verified by various characterization techniques. Noticeably, Fe₃O₄/PDVB showed efficient and fast adsorption rate to dye Rhodamine B, and the adsorption capacity reached 85.81 mg/g within 15 min. Moreover, the magnetic polymer can be easily separated by external magnetic field after adsorption and facilely recovered by ethanol extraction, which benefit its large-scale applications in the environmental protection, especially in the chemical accident remediation.     

Fe loaded mesocellular silica foam: role of acid and 1,3,5-trimethylbenzene concentrations on the catalyst and its performance in the degradation of acid red B

Various mesocellular foam silica based materials were successfully synthesized by varying acid (HCl) concentration and 1,3,5-trimethylbenzene (TMB) dosage and the surface and textural characteristics of the resulting materials were elucidated. TEM images demonstrated that the combination of low TMB dosage (0.5 g) and high HCl concentration (2.5 M) assigned as MCFA led to the formation of multilamellar vesicle structures that showed large pore diameters (7–8 nm) with lengthy channels. Meanwhile, the combination of low HCl concentration (0.5 g) and medium range of TMB dosage (2.0 g) assigned as MCFB produced silica supports with worm-like structures that had small pore diameters (4–5 nm) and short mesochannels. However, when high TMB dosage (3.0 g) was combined with medium concentration of HCl (1.5 M) to produce MCFC, the material had large pore diameter (6 nm) and large pore volume and surface area (1.833 cm³/g, 740 m²/g). It was obtained with the formation of foam-like structures that resembled mesostructured cellular foam. All the synthesized silica supports were then loaded with 5.4 wt% of Fe and their catalytic performance was tested based on the degradation of ARB dye at different initial concentrations (25, 50 and 100 mg/L) via Fenton-like process. Fe-MCFA and Fe-MCFC showed high degradation of ARB for all the concentrations tested. Meanwhile, Fe-MCFB catalyst demonstrated high degradation efficiency at 25 mg/L and slowly decreased when the initial concentration of dye was increased to 50 and 100 mg/L. The best performance was shown by Fe-MCFC that demonstrated both high catalytic activities (100 % decolourisation and 92 % COD removal) under a wide range of ARB dye concentrations (25–100 mg/L). The performance was attributed to the unique structure and large pores that enabled the reaction process to occur effectively regardless of the initial concentration of ARB dye. Fe-MCFC showed the least leaching of Fe into the solution (<0.5 mg/L) as well as high reusability and stability (could maintain 100 % decolourisation for up to three cycles). The least leaching of Fe was shown by Fe-MCFC and it could be attributed to the microenvironment of the catalyst.     

PRODUCTION AND CHARACTERIZATION OF POROUS CARBON FROM DATE PALM SEEDS BY CHEMICAL ACTIVATION WITH H3PO4: PROCESS OPTIMIZATION FOR MAXIMIZING ADSORPTION OF METHYLENE BLUE

The potential of date palm pits to be a suitable precursor for preparation of porous carbon was explored in the present work, utilizing phosphoric acid as the activating agent. Experimental methods reported in the literature were chosen with certain modifications in order to simplify the process. Process optimization was performed using the popular response surface methodology (RSM) adopting a Box-Behnken design. Process optimization was intended to maximize the porous carbon yield and the methylene blue (MB) adsorption capacity, with the process variables being the activation temperature, impregnation ratio (IR), and activation time. The structural characteristics were assessed based on nitrogen adsorption isotherms, SEM, and FT-IR, while the adsorption capacity was estimated using MB adsorption. The optimized experimental conditions were identified to be an activation temperature of 400°C, IR of 3, and activation time of 58 min, with the resultant porous carbon having a yield of 44% and MB adsorption capacity of 345 mg/g. The structural characteristics of the porous carbon reveal the BET surface area to be 725 m²/g, with pore volume of 1.26 cc/g, an average pore diameter of 2.91 nm, and total micropore volume of 0.391 cc/g. The popular Langmuir and Freundlich adsorption isotherm models were tested, and a maximum monolayer adsorption capacity of MB was estimated to be 455 mg/g, which compares with the highest for MB reported in literature, evidencing the suitability of porous carbon for adsorption of macromolecular compounds. The low activation temperature and activation time with highest yield render the process technically and economically attractive for commercial use.     

微波活化稻壳基生物质材料对亚甲基蓝的吸附性能

以KOH为活化剂,采用微波活化法处理农业废稻壳,制备生物质吸附材料,通过静态吸附实验考察了其对阳离子染料亚甲基蓝的吸附性能. 结果表明,所制生物质材料对亚甲基蓝的最大吸附量为109.9 mg/g,吸附过程符合伪二级动力学方程和Langmuir等温吸附模式,为快速吸附和单分子层吸附,膜扩散是速率控制步骤,吸附过程为生物质材料孔道内部物理吸附和O?H官能团吸附的共同作用.     

Size-controlled synthesis of mesoporous silica nanoparticles using rice husk by microwave-assisted sol–gel method

Mesoporous silica nanoparticles with distinct characteristics like particle size, tunable pores, and high surface area have received much interest for environmental remediation, energy conversion, and biological applications. In this work, we synthesized spherical silica nanoparticles with tunable particle size and mesoporous properties using a low-cost silica source (rice husk) and polyethylene glycol (PEG) via microwave-assisted sol–gel synthesis. The formation of an amorphous silica structure was found using XRD and FTIR analysis. FESEM analysis showed that altering the PEG concentration from .01 to .005 M produced spherical silica nanoparticles with 100–500 nm in size. Nitrogen adsorption–desorption demonstrated that silica nanoparticles obtained with .005, .007, and .01 M of PEG had unique pore sizes and distributions, with specific surface areas of 51.475, 62.367, and 84.251 m²/g, respectively. These results might be due to PEG molecules’ capping effect, which acts as a soft template to regulate particle size, pore size, and dispersion by interacting with sodium silicate precursor. Hence, this approach can be a facile and cost-effective method to prepare mesoporous silica nanoparticles with controllable nanoscale characteristics for suitable applications.     

Methylene blue adsorption from aqueous solutions to flexible poly(vinyl chloride) silica composites

Methylene blue (MB) adsorption studies were performed with poly(vinyl chloride)‐(dioctyl phthalate)‐silica composites, which were obtained by using plastisol‐plastigel technology. The films were flexible, having elastic modulus of 1.0–1.5 GPa. Diminishing MB concentration in the aqueous phase was followed as the adsorption process advanced by using visible spectroscopy. Contributions of the individual components of the composites to adsorption were also investigated. Although the MB adsorption capacity was extensively high for silica, it was moderate for the composite, most likely owing to the occlusion of pores of silica by plasticizer to some extent. The improvement of MB adsorption capacity of the composites as the silica ratio increased was explicitly deduced from the optical microscopy photographs. The diffusion coefficients of MB through the composites were 5 × 10^?13, 6 × 10^?13, and 3 × 10^?13 m² s^?1 with regression coefficients of 0.73, 0.89, and 0.88 for 0, 2, and 16% silica‐containing composites, respectively. Because of the slow diffusion of MB in poly(vinyl chloride)‐silica composites, using them as dynamic column adsorbent was not practical. However, these versatile plastics can be used as plastic labels, colored clothing, leather substitutes, antimicrobial medical devices, and laser printable surfaces. J. VINYL ADDIT. TECHNOL., 21:42–50, 2015. © 2014 Society of Plastics Engineers     

Radiation-initiated chitosan-based double network hydrogel: Synthesis,characterization, and adsorption of methylene blue

A novel chitosan (CTS)-based double network Poly(2-acrylaMido-2-Methyl-1-propanesulfonic acid)/Polyacrylamide/CTS hydrogel was synthesized by irradiation initiated. Laponite RD (RD) was used as both dopant and the cross-linking agent. Then the fabricated hydrogel was applied as an efficient adsorbent to remove the methylene blue (MB) in an aqueous solution. This hydrogel has both high strength and good adsorption properties for MB. The results from Brunauer–Emmett–Teller method confirmed that the hydrogel has a large specific surface area (96 m²/g) and developed pore structure, which is available for the contact between the adsorbent and dye molecules. In the adsorption process, the RD provides plenty of negative charges as adsorption sites for MB molecules. The influence of pH, temperature, and adsorbent dose on the adsorption performance was investigated in detail. The experimental data fit well with the pseudo-second-order kinetic model and Langmuir isotherm. Besides, the mechanical strength of the hydrogel was also investigated in this work.     

Macroporous rubber gels as reusable sorbents for the removal of oil from surface waters

Macroporous organogels were prepared by solution crosslinking various rubbers in benzene at ?18 °C. Butyl rubber (PIB), cis-polybutadiene (CBR) and styrene–butadiene rubber (SBR) were used as the rubber components, while sulfur monochloride was the crosslinker in the gel preparation. The organogel networks consist of large pores of 10¹–10² μm in size caused by the benzene crystals acting as a template during gelation. The networks formed by CBR and SBR showed an aligned porous structure consisting of regular pores, whereas those derived from PIB had irregular pores with a broad pore size distribution due to the phase separation of PIB chains at low temperatures. All organogels were very tough and could be completely compressed without any crack development. Sorption tests showed that the organogels were efficient at removing crude oil, gasoline, diesel, fuel oil and olive oil. The organogels are reusable once they are squeezed, leading to continuous sorption capacities of CBR or SBR gels for crude oil and olive oil of 33–38 g/g and 24–27 g/g, respectively. These sorption capacities are two to three times the capacity of the gels derived from PIB.     

Synthesis of mesoporous silica particles with controlled pore structure

Silica particles, with controllable porosity, were synthesized using two different precursors, tetraethylortosilicate (TEOS) and sodium silicate, but without the addition of template. Characteristics of silica particles (aggregates) prepared by these two methods were compared. The pore structure was tuned only by changing the processing parameters, such as precursor concentration, base concentration, temperature and reaction time. The pore structure of prepared silica particles (aggregates) is strongly influenced by processing conditions and easy controllable in broad range of the specific surface area, pore size, size distribution and pore volume. However, the silica particles synthesized from TEOS have very low total pore volume (ranging from 0.06 to 0.2 cm³/g) and a large portion of pores smaller than 4 nm. On the other side, the silica particles prepared from sodium silicate can be defined as a mesoporous silica with the average pore size up to 20 nm and much higher total pore volume (ranging from 0.8 to 1.5 cm³/g), which are important advantages for their application in encapsulation of enzymes.     

Soft-template synthesis of ordered mesoporous carbon/nanoparticle nickel composites with a high surface area

Ordered mesoporous carbon/nanoparticle nickel composites have been synthesized via multi-component co-assembly strategy associated with a direct carbonization process from resol, tetraethyl orthosilicate, Ni(NO₃)₂·6H₂O and triblock copolymer F127 and subsequent silicates removal with NaOH solution. The incorporation of rigid silicates in the pore walls can reduce framework shrinkage significantly during the pyrolysis process, creating large mesopores. Moreover, plenty of complementary small pores caused by silica removal are observed in the carbon pore walls, which contribute to the large surface area. The mesoporous carbon/nanoparticle nickel composites with a low Ni content (1.7 wt%) possess ordered two-dimensional hexagonal structure, large mesopores (6.8 nm), high surface area (1580 m² g⁻¹) and large pore volume (1.42 cm³ g⁻¹). Magnetic Ni nanocrystals with particle size of ∼16.0 nm are confined in the matrix of carbon frameworks. With increase of Ni content, the surface area and pore volume of the composites decrease. The particle size of metallic Ni nanocrystals increases up to 20.3 nm, when its content increases to 10 wt%. These carbon/nanoparticle nickel composites with high surface area, large pore size and superparamagnetic property show excellent adsorption properties for bulky dye fuchsin base and an easy separation procedure.     

Activated carbon from bacterial cellulose as an effective adsorbent for removing dye from aqueous solution

ABSTRACT

Novel activated carbon (AC) derived from bacterial cellulose (BC-AC) was produced by phosphoric acid activation at a carbonization temperature of 500 °C. BC-AC possesses mesoporous structures of 2.3 nm in diameter, porosity of 1.0 cm³/g and surface area of 1734 m²/g with high thermal stability between 100 and 500 °C. BC-AC could be used as an effective adsorbent for removing methylene blue (MB) from aqueous solutions with the maximum adsorption capacity of 505.8 mg/g. BC-AC presented physisorption and the adsorption of MB was most likely to be a monolayer adsorption. The Redlich–Peterson model displayed the best fit with the experimental data.     

Characterization of graphene oxide supported porous silica for effectively enhancing adsorption of dyes

ABSTRACT

This paper reported the synthesis of graphene oxide (GO)/mesoporous SBA-15 nanocomposite with excellent adsorption properties. The samples were characterized by XRD, FESEM, TEM, FTIR, Raman spectrometer, and surface area analyzer. The adsorption study implied that incorporating GO into SBA-15 frameworks displayed much higher adsorption capacity levels than did pure SBA-15. The composite displayed uniform pore size (6.50 nm), large pore volume (1.035 cm³/g), and high surface area (891 m²/g). The adsorption capacity of samples decreased with increasing sample dosage and adsorption temperature, and increasing initial concentration of dye. The maximum adsorption capacity of the composite for methylene blue was found to be 242 mg/g. The removal efficiency reached 100%. The proposed method was simple and suitable for mass production.