Polycondensation Of Formaldehyde Research Articles

Resorcinol-Formaldehyde-Derived Carbon Xerogels: Preparation, Functionalization, and Application Aspects.

Carbon xerogels (CXs) are materials obtained via the pyrolysis of resins prepared via the sol-gel polycondensation of resorcinol and formaldehyde. These materials attract great attention as adsorbents, catalyst supports, and energy storage materials. One of the most interesting features of CXs is the possibility of fine-tuning their structures and textures by changing the synthesis conditions in the sol-gel stage. Thus, the first part of this review is devoted to the processes taking place in the polycondensation stage of organic precursors. The formation of hydroxymethyl derivatives of resorcinol and their polycondensation take place at this stage. Both of these processes are catalyzed by acids or bases. It is revealed that the sol-gel synthesis conditions, such as pH, the formaldehyde/resorcinol ratio, concentration, and the type of basic modifier, all affect the texture of the materials being prepared. The variation in these parameters allows one to obtain CXs with pore sizes ranging from 2-3 nm to 100-200 nm. The possibility of using other precursors for the preparation of organic aerogels is examined as well. For instance, if phenol is used instead of resorcinol, the capabilities of the sol-gel method become rather limited. At the same time, other phenolic compounds can be applied with great efficiency. The methods of gel drying and the pyrolysis conditions are also reviewed. Another important aspect analyzed within this review is the surface modification of CXs by introducing various functional groups and heteroatoms. It is shown that compounds containing nitrogen, sulfur, boron, or phosphorus can be introduced at the polycondensation stage to incorporate these elements into the gel structure. Thus, the highest surface amount of nitrogen (6-11 at%) was achieved in the case of the polycondensation of formaldehyde with melamine and hydroxyaniline. Finally, the methods of preparing metal-doped CXs are overviewed. Special attention is paid to the introduction of a metal precursor in the gelation step. The elements of the iron subgroup (Fe, Ni, Co) were found to catalyze carbon graphitization. Therefore, their introduction can be useful for enhancing the electrochemical properties of CXs. However, since the metal surface is often covered by carbon, such materials are poorly applicable to conventional catalytic processes. In summary, the applications of CXs and metal-doped CXs are briefly mentioned. Among the promising application areas, Li-ion batteries, supercapacitors, fuel cells, and adsorbents are of special interest.

Nafion-Integrated Resorcinol-Formaldehyde Resin Photocatalysts for Solar Hydrogen Peroxide Production.

Photocatalytic generation of H2O2 from water and O2 is a promising strategy for liquid solar-fuel production. Previously reported powder photocatalysts promote a subsequent oxidative/reductive decomposition of the H2O2 generated, thereby producing low-H2O2-content solutions. This study reports that Nafion (Nf)-integrated resorcinol-formaldehyde (RF) semiconducting resin powders (RF@Nf), synthesized by polycondensation of resorcinol and formaldehyde with an Nf dispersion solution under high-temperature hydrothermal conditions, exhibit high photocatalytic activities and produce high-H2O2-content solutions. Nf acts as a surface stabilizer and suppresses the growth of RF resins. This generates small Nf-woven resin particles with large surface areas and efficiently catalyze water oxidation and O2 reduction. The Nf-woven resin surface, due to its hydrophobic nature, hinders the access of H2O2 and suppresses its subsequent decomposition. The simulated-sunlight irradiation of the resins in water under atmospheric pressure of O2 stably generates H2O2, producing high-H2O2-content solutions with more than 0.06 wt % H2O2 (16 mM).

Removal of Cs-137 Radionuclide by Resorcinol-Formaldehyde Ion-Exchange Resins from Solutions Simulating Real Liquid Radioactive Waste.

The efficiency of the removal of Cs-137 radionuclides with porous and non-porous resorcinol-formaldehyde resins from alkaline solutions simulating the composition of real liquid radioactive waste (LRW) streams has been evaluated. Resins were synthesized through the polycondensation of resorcinol and formaldehyde in an alkaline medium at a molar ratio of 1.8/2.2 and a temperature of 210 °C. The Cs-137 distribution coefficients on RFRs in alkaline solutions simulating LRW were above 103 mL/g under static sorption conditions. In a model solution with pH 11, the full dynamic sorption capacity of non-porous RFR was 0.178 mmol/g. The values of the full dynamic sorption capacities of porous RFRs were 0.274 and 1.035 mmol/g for resins obtained with calcium carbonate and toluene as templates, respectively. When the sizes of RFR beads increased two-fold, the volume until 5% cesium breakthrough decreased by 20-40%. The most pronounced beneficial effect of the RFR's porosity was observed at flow rates from 25 to 50 BV/h. It was shown that the negative effect of metal cations on Cs-137 uptake increases in the following order: Na+ < Mg2+ < Ca2+ < K+. The number of bed volumes of LRW-simulating solution decontaminated with RFRs until 5% cesium breakthrough was above 450; that is higher than the value of known commercially available analogs. The latter shows that the developed RFRs are promising for application in technological schemes of alkaline LRW processing.

Amine-Modified Carbon Xerogels as Effective Carbon-Based Adsorbents of Anionic Dye from Aqueous Solutions.

Carbon xerogels were obtained by polycondensation of resorcinol and formaldehyde in a water medium. Their surface was oxidized by ammonium persulfate and then modified with amine groups. Four amines were used: methylamine, ethylamine, propylamine, and ethylenediamine, differing in carbon chain length and number of amine groups. The materials were characterized by low-temperature nitrogen sorption, elemental analysis, thermal analysis, X-ray diffraction, infrared spectroscopy, and determination of the surface oxygen group content with the use of the Boehm method. The final carbon adsorbents had surface areas ranging from 172–663 m2/g and acid–base nature. They were applied for adsorption of thymol blue from water solution. The sorption capacities of the studied adsorbents ranged from 83 to 140 mg/g. The presence of amine groups on the xerogel surface was found to increase its sorption capacity towards the dye studied. The dye adsorption process is endothermic and spontaneous, as indicated by the positive values of ΔH and the negative values of ΔG, respectively. The kinetics of adsorption of thymol blue was established to be described by the pseudo-second-order model. The equilibrium data were analyzed by the Langmuir and Freundlich models. The character of thymol blue adsorption is much better described by the Langmuir isotherm.

Studying the characteristics of iodine sorption in synthetized ion-exchangers

Iodine is an essential micronutrient for humans and animals due to its important role as a component of thyroid hormones. Kazakhstan is a country, most regions of which suffer from a natural deficiency of iodine. At the same time, the country has a rich resource base for obtaining iodine and its compounds. These are formation waters of oil fields under development containing 0.001–0.005% iodine. To extract iodine from natural oil-field brines, we have proposed ion-exchange materials obtained from the waste of the oil refining industry. The article presents the results of studying the characteristics of iodine sorption in the synthesized ion exchangers. The synthesis of ion exchangers was carried out by polycondensation of dihydric phenols (1,3 dioxybenzene, 1,2 dioxybenzene, 1,4 dioxybenzene), hexamethylenediamine, and formaldehyde. The following sorption characteristics of iodine by the synthesized ion exchangers were studied: the influence of the pH of a solution on iodine sorption; kinetic curves of iodine sorption; iodine sorption isotherms; mechanism of iodine sorption. It has been established that the sorption of iodine on the synthesized samples is essentially independent of the pH of a medium, and the degree of its extraction in the entire area under study is 94–100%. Studies have been carried out on the dependence of the degree of extraction and the logarithm of the iodine distribution coefficient on the duration of the process. The sorption capacity of the synthesized ion exchangers with respect to iodine was estimated depending on the structure of the ion exchanger and sorption conditions. It has been established that sorbents based on 1,4 dioxybenzene, which are distinguished by high kinetic abilities and static exchange capacity (SEC = 2283.88 mg/g), are most preferable for iodine extraction. The mechanism of sorption of iodine by synthesized ion exchangers has been determined.

SYNTHESIS AND STUDY OF A COMPLEXING SORBENT, BASED ON UREA, FORMALDEHYDE AND AMINOACETIC ACID, USING IR SPECTROSCOPYAND SCANNING ELECTRON MICROSCOPE

The article presents the formula of the polyampholyte, synthesized by us -an ion-exchange sorbent (UFA), obtained by the reaction of polycondensation of urea, formaldehyde and aminoace-tic acid. The effect of pHmedium and reaction temperature on the molecular weight of the resulting polymer product was studied. The conditions for its synthesis are compared with the conditions for obtaining previously studied ion-exchange polyampholytes of the same type. The IR spectra of pol-yampholyte complexes with some d-elements: copper, nickel, zinc, cobalt and cadmium ions were registered and studied for the first time. These spectra are compared with the spectra of the poly-ampholyte itself, the ligand. It has been established that the synthesized sorbent contains intra and intermolecular hydrogen bonds of hydroxyl groups, methylene fragments -CH2-, carbonyl groups -C=O both in the ring and in the main chain, vibrations of bound OH groups. The presence of amide nitrogen in the polymer chain was shown. Based on the IR spectra, a scheme is presented for the synthesis of polyampholyte by polycondensation of the initial reagents: formaldehyde, urea (carbamide) and aminoacetic acid (glycine). Some physicochemical properties and results of ele-mental analysis of the coordination compounds of the resulting polyampholyte with five d-metal ions (Cu(II), Zn(II), Ni(II), Co(II), Cd(II)) are presented. Based on the analysis of the IR spectra of the complexes and their elemental analysis, a general structural formula of MFA complex com-pounds with the indicated ions was suggested. The surface structure of the resulting polyampholyte was studied by scanning electron microscopy (SEM analysis). The images obtained by this method indicate that this ion exchanger has a very good high sorption capacity or the ability to absorb various metal ions.

Synthesis of Lignosulfonate-Based Dispersants for Application in Concrete Formulations.

Lignosulfonates (LS) are products from the sulfite pulping process that could be applied as renewable environmentally-friendly polymeric surfactants. Being widely used as plasticizers and water-reducing admixtures in concrete formulations LS compete in the market with petroleum-based superplasticizers, such as naphthalene sulfonate formaldehyde polycondensate (NSF) and copolymer polycarboxylate ethers (PCE). In this work, different chemical modification strategies were used to improve LS performance as dispersants for concrete formulations. One strategy consisted in increasing the molecular weight of LS through different approaches, such as laccase and polyoxometalate-mediated polymerization, glyoxalation, and reversible addition-fragmentation chain transfer (RAFT) polymerization. The other strategy consisted of preparing LS-based non-ionic polymeric dispersants using two different epoxidized oligomer derivatives of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG). Modified LS were used to prepare cement pastes, which were examined for their fluidity. Results revealed that the most promising products are PPG-modified LS due to the introduction of PPG chains by reaction with phenolic moieties in LS. The enhanced dispersant efficiency of the ensuing products is probably related not only to electrostatic repulsion caused by the sulfonic ionizable groups in LS but also to steric hindrance phenomena due to the grafted bulky PPG chains.

Carbon xerogels combined with nanotubes as solid-phase extraction sorbent to determine metaflumizone and seven other surface and drinking water micropollutants

Carbon xerogels (CXs) were synthesized by polycondensation of resorcinol and formaldehyde, followed by thermal annealing, and subjected to hydrothermal oxidation. Solid-phase extraction (SPE) cartridges were filled with CXs and tested for extraction of metaflumizone and other seven environmental micropollutants (acetamiprid, atrazine, isoproturon, methiocarb, carbamazepine, diclofenac, and perfluorooctanesulfonic acid) before chromatographic analysis. The recoveries obtained with the pristine CX were low for most analytes, except for metaflumizone (69 ± 5%). Moreover, it was concluded that the adsorption/desorption process of the micropollutants performed better on CXs with a less acidic surface (i.e., pristine CX). Thus, cartridges were prepared with pristine CX and multi-walled carbon nanotubes (MWCNTs) in a multi-layer configuration. This reusable cartridge was able to simultaneously extract the eight micropollutants and was used to validate an analytical methodology based on SPE followed by ultra-high performance liquid chromatography-tandem mass spectrometry. A widespread occurrence of 6/8 target compounds was observed in surface water collected in rivers supplying three drinking water treatment plants and in the resulting drinking water at the endpoint of each distribution system. Therefore, the first study employing CXs and MWCNTs as sorbent in multi-layer SPE cartridges is herein reported as a proof of concept for determination of multi-class water micropollutants.

Tailoring Properties of Resol Resin-Derived Spherical Carbons for Adsorption of Phenol from Aqueous Solution.

The polycondensation of resorcinol and formaldehyde in a water–ethanol mixture using the adapted Stöber method was used to obtain resol resins. An optimization of synthesis conditions and the use of an appropriate stabilizer (e.g., poly(vinyl alcohol)) resulted in spherical grains. The resins were carbonized in the temperature range of 600–1050 °C and then chemically activated in an aqueous HNO3 solution, gaseous ammonia, or by an oxidation–reduction cycle (soaking in a HNO3 solution followed by treatment with NH3). The obtained carbons were characterized by XRD, the low-temperature adsorption of nitrogen, SEM, TGA, and XPS in order to determine degree of graphitization, porosity, shape and size of particles, and surface composition, respectively. Finally, the materials were tested in phenol adsorption. The pseudo-second order model perfectly described the adsorption kinetics. A clear correlation between the micropore volume and the adsorption capacity was found. The content of graphite domains also had a positive effect on the adsorption properties. On the other hand, the presence of heteroatoms, especially oxygen groups, resulted in the clogging of the pores and a decrease in the amount of adsorbed phenol.

Effect of starch as binder in carbon aerogel and carbon xerogel preparation

Carbon aerogels and carbon xerogels were synthesized through resorcinol – formaldehyde polycondensation using Na2CO3 as catalyst. The effect of soluble starch introduction in the organic gel preparation on the porous surface properties of these materials was studied. The role of the drying process of the organic gels on the changes in the surface and structural properties of these materials after the addition of soluble starch is discussed. The presence of starch in the prepared carbon xerogels results in the development of microporosity while maintaining the characteristic mesoporosity of carbon xerogels. The Brunauer – Emmett -Teller (BET) surface area increases from 309 m2/g in carbon xerogel without soluble starch until 685 m2/g when 10% of soluble starch is added. The R- value and average crystallite lattice parameters, inter-layer spacing, crystallite height, crystallite diameter and the average number of aromatic layers per carbon crystallite are discussed in function of drying step and presence of soluble starch. The surface properties were also studied by Raman and DRIFT spectroscopies.

Compact energetic crystals@ urea-formaldehyde resin micro-composites with evident insensitivity

Abstract To improve the safety of nitramine explosives, two compact urea-formaldehyde (UF) resin coating micro-composites were fabricated via poly-condensation of urea and formaldehyde on the surfaces of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexazisowurtzitane (HNIW) in this study. The two core-shell composites were characterized by several methods and their sensitivities were also studied. The results indicated that the UF resins were compactly coated on the surfaces of HMX and HNIW crystals with low contents, and the UF resin coating can stabilize the polymorphs and change the thermal properties of energetic crystals remarkably. In addition, the impact sensitivity of core-shell energetic composites reduced significantly comparing with pure explosives and corresponding explosive coated by other amino-resins, attributing to the buffering effect and better flexibility of UF resin.

Carbon aerogels with oxygen-containing surface groups for use in supercapacitors

We prepared a series of modified carbon aerogels with oxygen-containing functional groups through a sol–gel process by polycondensation of phloroglucinol, resorcinol and formaldehyde using starch addition. The effect of starch addition on the pore structure and electrochemical performance of the carbon aerogels was investigated. Carbon aerogels were characterized by scanning-electron microscopy, transmission-electron microscopy, surface-area analysis, X-ray diffractometry, Raman spectrometry and X-ray photoelectron spectroscopy. The electrochemical properties were studied by using cyclic voltammetry, galvanostatic charge–discharge measurements and electrochemical impedance spectroscopy. When the starch addition was 25 wt%, the as-prepared sample had a specific surface area of 734 m2 g−1 and an outstanding specific capacitance of 147 F g−1 at 1.0 A g−1. The as-prepared carbon aerogels exhibited a high coulombic efficiency and a stable cycle life at a current density of 1.0 A g−1 over 1000 cycles. This ideal performance was attributed to the addition of starch, which was beneficial for the application of carbon aerogels in supercapacitors.

Facile Preparation of Carbon Aerogels with Different Drying Methods

Carbon aerogels were prepared through a polycondensation of phloroglucinol, resorcinol and formaldehyde with sodium carbonate as the catalyst under different drying methods. The drying methods were room temperature drying, vacuum drying and freeze drying. The effects of different drying methods on the porous structure of carbon aerogels were studied systematically. The texture and pore structure were investigated under scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and a surface-area analyzer. The results show that the freeze-drying method was good for the specific surface area of carbon aerogels, up to 843 m2 g–1.

Tunable and Processable Shape-Memory Materials Based on Solvent-Free, Catalyst-Free Polycondensation between Formaldehyde and Diamine at Room Temperature.

Compared with traditional thermosets, malleable thermosets have more applications in aerospace, biotechnology, and construction. Here we report a one-step, solvent-free, catalyst-free polycondensation method between diamine and formaldehyde to prepare a series of malleable hemiaminal dynamic covalent networks (HDCNs). The materials have excellent malleability and reprocessability by hot pressing. The Young's modulus and breaking strength of HDCNs obtained by the polycondensation of formaldehyde and 4,4-diaminodiphenylmethane (MDA) are as high as 1.6 GPa and 60 MPa, respectively, which can be facilely adjusted through the introduction of polyetheramine-400 (PEDA). Moreover, the HDCNs feature the shape memory ability with a recovery ratio above 93.5% and can be recycled by the addition of different monomers. This promising HDCN, prepared from economical raw materials, may have vast applications in industries.

Пионеры синтеза ионообменных материалов. 120 лет со дня рождения Александра Борисовича Даванкова (1899-1971)

Представлена история создания отечественных ионообменников с конца 1930 гг. по начало 1970 гг. на основе анализа работ лаборатории ионитов МХТИ им. Д.И. Менделеева. Представлена биография Александра Борисовича Даванкова – одного из отечественных пионеров ионного обмена, а также ранее неизвестные факты биографий и научные работы некоторых ученых, внесших заметный вклад в данную область. Впервые проанализированы ключевые публикации и патенты этого периода с историко-научной точки зрения.

Synthesis and application of additives based on cardanol as demulsifier for water-in-oil emulsions

Emulsion formation is one of the most important problems faced by petroleum companies to guarantee the flow of fluids during petroleum production, once its formation is often associated to the colloidal state of asphaltenes in petroleum. For this reason, chemical additives should be frequently used to stabilize the asphaltenes and reduce or prevent emulsion formation. Unfortunately, it does not exist any widespread chemical compound that could be used for petroleum reservoirs indistinctly. Consequently, scanning and screening analysis for new compounds should be performed with the purpose to find more efficient and eco-friendlier demulsifiers. In this paper, four different chemical routes (hydrogenation, ethoxylation, formaldehyde polycondensation, and ethoxylation of formaldehyde polycondensation) have been used to synthetize four new products from cardanol to evaluate their activity as demulsifier agents. These additives were characterized by FTIR and 1H NMR analysis. The demulsification activity were studied in emulsions using three Brazilian crude oil produced with a 30% (v/v) brine cut, 60 and 240 g/L NaCl of salinity, at different pH (range from 3 to 10), under agitation (3200 rpm). Bottle test was carried out at 60 °C in graduated tubes for water separability tests, by adding a constant composition (200 ppm) of each chemical tested. The results show that demulsification is more significant for ethoxylated compounds, at neutral pH.

The feasibility of energy extraction by carbon xerogel electrodes – A question of ionizable or redox active surface groups?

Carbon Xerogel electrodes' materials were prepared by polycondensation of resorcinol and formaldehyde. They show accommodation of anions in preference to cations by their porous structure. In addition, their selectivity toward anion electroadsorption was found to be pH dependent, with an increase in electrodes' capacitance in acidic solutions.This dependence of the capacitance on the pH of the solution is explained by the presence of functional carboxylic surface groups in the Xerogel carbon micropores, determined by Boehm titration to be 3.26 meq/g. These functional surface groups give rise to the Donnan exclusion effect, whereby they cause partial repulsion of anions from the microporous structure. When the pH of the electrolyte solution is acidic (<2), most of these acidic functional surface groups are in their non-ionized state, and hence anions can freely penetrate the Xerogel carbon microporous structure.The pH dependent capacitance of these carbons was utilized to examine the feasibility of energy extraction from mixing of saline and acidic solutions following the four basic steps of capacitive mixing processes – charge, solution exchange, discharge, and another solution exchange. As opposed to what we expected, a potential rise was observed when the solution was exchanged from acidic to saline, rather than during the other exchange, from saline to acidic solution.It appears that upon exchange of the solutions from saline to acidic, the expected potential rise resulting from the change in the electrodes capacitance, is cancelled by the new quinone-hydroquinone equilibrium that is established on the electrodes by their surface groups. The ability of these surface redox functional groups to store charge provides a basis for energy extraction from the neutralization of acidic solutions, as described herein.

Kinetics of resorcinol–formaldehyde polycondensation by DSC

The kinetics of resorcinol–formaldehyde polycondensation was investigated by DSC. The resorcinol–formaldehyde polycondensation mixtures were prepared using different catalyst (Na2CO3) concentrations (molar ratio of resorcinol/catalyst R/C = 25 and 50) and mass contents of reactants (w = 20 and 40%). The studied polycondensation mixtures were heated from 10 to 100 °C at five different heating rates (0.5–2.5 °C min−1). The two obtained DSC peaks correspond with two reaction steps (formation of hydroxymethyl derivatives of resorcinol and polycondensation reaction itself). The overall reaction heat evolved during both steps corresponds to 97–104 kJ mol−1 for all mixtures. Based on the kinetic analysis, the first reaction step is best fitted by the second-order kinetic model and its rate is controlled by chemical reaction. The second reaction step can be described by R3 mechanism and is probably limited by diffusion in more viscous solution. Found kinetics equation allows to predict the composition of reaction mixture during the polycondensation at least at micro-scale. The obtained results can be useful for prediction of reaction course which can control the porosity of resorcinol–formaldehyde gels.

Synthesis, structure, and properties of bisphenol A formaldehyde sol—precursor of low-density aerogel

Low-density organic aerogels (down to 11–12 mg/cm3) were successively synthesized by polycondensation of formaldehyde with bisphenol A (2,2-diphenylolpropane or BPhA) methylol derivatives by the thermal treatment under basic conditions. In this paper, the main features of bisphenol A-formaldehyde (BF) sol and hydrogel formation have been examined for the first time. The molecular weight distribution both of the initial resin and the soluble products of its thermal processing were studied by size exclusion chromatography. A detailed study of the structure of sols and the dynamics of its change was carried out by dynamic and static light scattering and scanning and transmission electron microscopy. The results obtained allowed to describe the process of gel formation as a diffusion-limited cluster-cluster fractal aggregation of sol nanoparticles formed during the polycondensation. Crosslinking of low-density fractal aggregates leads to the formation of a macro-porous structure with a high pore volume and, ultimately, to a low-density aerogel.

Structure Manipulation of Carbon Aerogels by Managing Solution Concentration of Precursor and Its Application for CO2 Capture

A series of carbon aerogels were synthesized by polycondensation of resorcinol and formaldehyde, and their structure was adjusted by managing solution concentration of precursors. Carbon aerogels were characterized by X-ray diffraction (XRD), Raman, Fourier transform infrared spectroscopy (FTIR), N2 adsorption/desorption and scanning electron microscope (SEM) technologies. It was found that the pore structure and morphology of carbon aerogels can be efficiently manipulated by managing solution concentration. The relative micropore volume of carbon aerogels, defined by Vmicro/Vtol, first increased and then decreased with the increase of solution concentration, leading to the same trend of CO2 adsorption capacity. Specifically, the CA-45 (the solution concentration of precursors is 45 wt%) sample had the highest CO2 adsorption capacity (83.71 cm3/g) and the highest selectivity of CO2/N2 (53) at 1 bar and 0 °C.