Enhanced electrocatalytic removal of bisphenol a by introducing Co/N into precursor formed from phenolic resin waste

Bisphenol A (BPA) is a typical endocrine disruptor, which can be used as an industrial raw material for the synthesis of polycarbonate and epoxy resins, etc. Recently, BPA has appeared on the list of priority new pollutants for control in various countries and regions. In this study, phenolic resin waste was utilized as a multi-carbon precursor for the electrocatalytic cathode and loaded with cobalt/nitrogen (Co/N) on its surface to form qualitative two-dimensional carbon nano-flakes (Co/NC). The onset potentials, half-wave potentials, and limiting current densities of the nitrogen-doped composite carbon material Co/NC in oxygen saturated 0.5 mol H2SO4 were -0.08 V, -0.61 V, and -0.41 mA cm-2; and those of alkaline conditions were -0.65 V, -2.51 V, and -0.38 mA cm-2, and the corresponding indexes were improved compared with those of blank titanium electrodes, which indicated that the constructed nitrogen-doped composite carbon material Co/NC was superior in oxygen reduction ability. The catalysis by metallic cobalt as well as the N-hybridized active sites significantly improved the efficiency of electrocatalytic degradation of BPA. In the electro-Fenton system, the yield of hydrogen peroxide generated by cathodic reduction of oxygen was 4.012 mg L-1, which effectively promoted the activation of hydroxyl radicals. The removal rate of BPA was above 95% within 180 min. This work provides a new insight for the design and development of novel catalyst to degrade organic pollutants.

Preparation of spherical porous carbon from lignin-derived phenolic resin and its application in supercapacitor electrodes

Lignin is the most abundant aromatic biomass resource in nature and is the main by-product of paper industry and biorefinery industry, which has the characteristics of abundant source, renewable and low cost. Deep eutectic solvents (DES) are a nascent environmentally friendly solvent option that is gaining traction. DES composed of p-toluenesulfonic acid and choline chloride is used for batch treatment of alkaline lignin, and the bio-oil obtained is ternary polymerized with formaldehyde and phenol to obtain lignin phenolic resin. The porous carbon material is produced through a two-step carbonization process, utilizing phenolic resin derived from lignin as the primary source of carbon. The morphology and composition of the carbon were analyzed by SEM, TEM, XRD, TGA, XPS and Raman spectroscopy, the specific surface area and pore size distribution were analyzed by BET. The results showed that the specific surface area of the lignin-based phenolic resin was significantly higher than that of the pure phenolic resin carbon, and the porous carbon material that was acquired demonstrated a specific surface area of as much as 1026 m2/g. In the three-electrode system, the specific capacitance of DLPFC can reach 245.8 F/g (0.25 A/g), with a very small decrease in the value of specific capacitance at 10,000 cycles, with a retention of 97.62% (10 A/g). The porous carbon demonstrated a specific capacitance of 112.4 F/g at a current density of 0.5 A/g, and the capacitance retention rate could still reach 98.8% after 5000 charge/discharge cycles, with high cycling stability (in the two-electrode system). The prepared symmetrical supercapacitors exhibited high energy density and power density of 3.9 Wh/kg and 125.0 W/kg. The results suggest a new idea of high value-added application of lignin phenolic resin for high-performance supercapacitor electrodes.

NIR Clusteroluminescence of Non-conjugated Phenolic Resins Enabled by Through-Space Interactions

Clusteroluminescence (CL) and through-space interactions (TSIs) of non-conjugated molecules have drawn more attention due to their unique photophysical behaviors that are different from largely conjugated luminogens. However, achieving red and even near-infrared (NIR) emission from such systems is still challenging due to the intrinsic drawbacks of non-conjugated molecules and the lack of theories for structure-property relationships. In this work, six phenolic resins are designed and synthesized based on two molecule-engineering strategies: increasing the number of TSIs units and introducing electron-donating/-withdrawing groups. All phenolic resins are verified as luminogens with CL property (CLgens), and the first example of CLgens with NIR emission (maximum emission wavelength ≥ 680 nm) and high absolute quantum yield (47%) is reported. Experiments and theoretical analysis reveal that two TSIs types, through-space locally excited state and through-space charge transfer state, play essential roles in achieving CL from these non-conjugated polymers, which could be manipulated via changing structural conformation and electron density or altering electron transition behaviors. This work not only provides an approach to manipulate TSIs and CL of non-conjugated polymers but also endows commercially available phenolic resins with high practical value as luminescence materials.

Ambient Preparation of Benzoxazine-based Phenolic Resins Enables Long-term Sustainable Photosynthesis of Hydrogen Peroxide

Rational design of polymer structures at the molecular level promotes the iteration of high-performance photocatalyst for sustainable photocatalytic hydrogen peroxide (H2O2) production from oxygen and water, which also lays the basis for revealing the reaction mechanism. Here we report a benzoxazine-based m-aminophenol-formaldehyde resin (APFac) polymerized at ambient conditions, exhibiting superior H2O2 yield and long-term stability to most polymeric photocatalysts. Benzoxazine structure was identified as the crucial photocatalytic active segment in APFac. Favorable adsorption of oxygen/intermediates on benzoxazine structure and commendable product selectivity accelerated the reaction kinetically in stepwise single-electron oxygen reduction reaction. The proposed benzoxazine-based phenolic resin provides the possibility of production in batches and industrial application, and sheds light on the de novo design and analysis of metal-free polymeric photocatalysts.

Hydrophilic tyrosine-based phenolic resin with micro-ripples morphology for marine antifouling application

Since biofouling challenges negatively influence the marine and transportation industries, developing effective antifouling materials have attracted extensive concern. A tyrosine-based antifouling phenolic resin (TPP resin) was synthesized using tyrosine as a natural phenol source. TPP exhibited shell-like surface morphology with micro-ripples and excellent anti-adhesion properties against bacteria and diatom. The micro-ripples surface might be caused by the strong hydrogen bonding or ionic interaction among tyrosine units resulting in microphase separation during the curing process. Tyrosine content in TPP resin has a great influence on the surface properties, morphology and antifouling characteristics. The higher the tyrosine content, the higher is the surface hydrophilicity, the denser and more regular is the micro-ripples morphology, and the stronger is the antifouling performance. TPP-60 % exhibited the best antifouling performance. Combination of the surface hydrophilicity and regular micro-ripples surface morphology afford TPP excellent antifouling performance. TPP resins offer a broad prospect for developing phenolic resin in the antifouling field.

Magnetic phenolic resin core-shell structure derived carbon microspheres for ultrafast magnetic solid-phase extraction of triazine herbicides

In this study, monodisperse magnetic carbon microspheres were successfully synthesized through the carbonization of phenolic resin encapsulated Fe₃ O₄ core-shell structures. The magnetic carbon microspheres showed high performance in ultrafast extraction and separation of trace triazine herbicides from environmental water samples. Under optimized conditions, both the adsorption and desorption processes could be achieved in 2 min, and the maximum adsorption capacity for simazine and prometryn were 387.6 and 448.5 μg/g. Coupled with HPLC-UV detection technology, the detection limit of triazine herbicides was in the range of 0.30-0.41 ng/mL. The mean recoveries ranged from 81.44 to 91.03% with relative standard deviations lower than 7.47%. The excellent magnetic solid phase extraction performance indicates that magnetic carbon microspheres are promising candidate adsorbent for the fast analysis of environmental contaminants. This article is protected by copyright. All rights reserved.

Conversion of phenolic mixture to refractory resins: A resourcezation strategy for phenolic distillation residues

A new resourcezation way has been proposed to address the treatment challenges of the light phenolic distillation residue (LPDR) from the coal-based phenolic distillation residue. Herein, the LPDR, which was collected at 20 kPa and 220 °C from the phenolic distillation residue, has been further used to synthesize the phenolic resin (named as RPF) for MgO-C refractories. It is found that the conversion efficiency of crude phenol mixture to RPF is 71.3%, which is lower than that of pure phenol. To increase the conversion efficiency and improve the properties of RPF, the crude phenolic mixture was blended with pure phenol for the synthesis. The optimal addition mass ratio of phenol in the crude phenol mixture (phenol/total phenolic compounds) is determined to be 0.8, where the obtained RPF could satisfy or even better than the national standard. Further addition of 10 wt% of urotropine (HMTA) as curing agent and 9 wt% of ferrocene (Fc) as modifier (named as MRPF) are found to significantly improve the graphitization of RPF. Under these conditions, the DTG at temperature of maximum mass lose rate (T_max) of MRPF was lower than that of commercial resin. The graphitization level was as high as 61.6% with the residual carbon rate up to 41.4%, which are higher than those of national standard. These findings provide insights for the resourcezation of the phenolic distillation residue.

Hydrophilic deep eutectic solvents modified phenolic resin as tailored adsorbent for the extraction and determination of levofloxacin and ciprofloxacin from milk

A reliable and efficient method for the simultaneous extraction and determination of antibiotics of ciprofloxacin and levofloxacin from milk was developed with solid phase extraction based on tailored adsorbent materials of deep eutectic solvents modified phenolic resin (DES-R-SPE). Six types of polyhydric alcohol-based hydrophilic DESs were prepared to modify the phenolic resin with the compositions of 3-aminophenol as a functional monomer, glyoxylic acid as a crosslinker, and polyethylene glycol 6000 as a porogen. And the prepared DES-Rs showed better extraction capacities for the target analytes than the unmodified phenolic resin because of more hydrogen bonding and electrostatic interactions supplied by DESs. The choline chloride-glycerol-based resin (DES¹-R) with the highest adsorption amounts was selected and the adsorption behavior of it was studied with static adsorption and the dynamic adsorption performance; the adsorption process followed Freundlich isotherm (R² ≥ 0.9337) and pseudo-second-order (R² ≥ 0.9951). The present DES¹-R-SPE method showed good linear range from 0.5 to100 μg mL^-1 (R² ≥ 0.9998), good recoveries of spiked milk samples (LEV, 96.7%; CIP, 101.5%), and satisfied repeatability for intra-day and inter-day (LEV, RSD≤5.4%; CIP, RSD≤4.6%).

Formaldehyde-free self-polymerization of lignin-derived monomers for synthesis of renewable phenolic resin

Most phenolic resins are synthesized with non-renewable petroleum-based phenol and formaldehyde, which have adverse effects on the environment and human health. To achieve green and sustainable production of phenolic resins, it is important to replace non-renewable toxic phenol and formaldehyde. Herein, a new strategy was proposed to completely replace phenol and formaldehyde, using lignin-derived monomers to synthesize renewable phenolic resins. Lithium aluminum hydride was utilized to reduce lignin-derived monomers, including vanillin, methyl vanillate, and syringaldehyde, to generate the corresponding vanillyl and syringic alcohol. With oxalic acid as the catalyst, vanillyl and syringic alcohol could be polymerized to phenolic resins without using formaldehyde. The structure of the phenolic resins based on lignin-derived monomers was analyzed by Fourier transform infrared spectroscopy and ¹³C and ³¹P nuclear magnetic resonance spectroscopy. Differential scanning calorimetry and thermogravimetric analysis were performed to characterize the thermal properties of the phenolic resins. The phenolic resins based on lignin-derived monomers exhibited excellent adhesion strength (6.14 MPa), glass transition temperature (T_g) (107-115 °C), and thermal stability, and its performance was similar to that of the commercial Novolak phenolic resin. This study presents a promising green and sustainable approach to synthesize renewable phenolic resins based on lignin-derived monomers without using formaldehyde.

Formation of highly graphitic char derived from phenolic resin carbonization by Ni-Zn-B alloy

The formation of highly graphitic phenolic resin chars (GPFCs) during catalytic carbonization at relatively low reaction temperature (1200-1600 °C) using novel Ni-Zn-B alloy catalyst with small amount of addition (5-15%) was systematically studied. Only two kinds of graphites (turbostratic graphite and ordered graphite) can be found in GPFCs after catalytic carbonization with Ni-Zn-B and their proportions were changed with reaction conditions. When Ni-Zn-B was involved at 1200-1600 °C, the phenolic resin char was fully transformed to be graphite, and ordered graphite content increased to 28.42% at 1400 °C, which was also almost twice of ordered graphite content in the char catalyzed by pure Ni. But the order graphite content would decrease due to sintering at higher reaction temperature. The addition of Zn and B can promote nickel-based alloy catalytic action by reducing melt point and accelerating graphitization respectively. It was also found that ordered graphite content could be used as a key evaluation parameter to directly reflect the quality of GPFCs based on detailed characteristics analysis. The model between three reaction conditions (reaction temperature, retention time, catalyst content) and ordered graphite content was built with artificial neural network (ANN), and the prediction accuracy of ANN was high up to 91.48%.

Facile synthesis of hierarchical mesopore-rich activated carbon with excellent capacitive performance

Mesoporous carbons attract increasing attention owing to their potential applications in supercapacitors. So far, controlled synthesis of mesoporous carbons with a narrow pore size distribution relies largely on the complicated template methods. To avoid the use of templates, a surfactant-free emulsion polymerization method is presented for the fabrication of a melamine-modified phenolic resin microrod (MPRR) assembled by micron-sized spherical cells and thin walls. In addition, one-step KOH activation strategy is adopted to synthesize hierarchical mesoporous activated carbon with 2-10 nm narrow mesopores by using MPRR as carbon precursors. The as-prepared mesoporous activated carbon has a high specific surface area of about 2758 m² g^-1 and a mesopore volume of 0.54 cm³ g^-1 (calculated by density functional theory), comprising ∼43.5% of total pore volume (∼1.43 cm³ g^-1). Hierarchical mesopores can significantly accelerate ion transfer and increase micropore accessibility, which endow the carbon with high specific capacitance equal to 409 F g^-1 at 0.1 A g^-1 and 268 F g^-1 at 100 A g^-1 in 6 M KOH electrolyte, with a high capacitance retention of 66%. Moreover, the assembled symmetric supercapacitor also exhibits good cycling stability in KOH electrolyte and delivers high power density equal to 12080 W kg^-1 when energy density is 5.02 Wh kg^-1. This finding provides an insight into directional tailoring of mesoporous structures of phenolic resin-based carbon materials at the molecular level for high-performance supercapacitors.

Multilayer bacterial cellulose/resole nanocomposites: Relationship between structural and electro-thermo-mechanical properties

The aim of this research was to fabricate multilayer insulator nanocomposites using phenolic resin impregnated bacterial cellulose (BC) handsheets and investigate the relationships between their structural and electro-thermo-mechanical properties. G. xylinus was incubated in a static Hestrin-Schramm culture at 28 °C for 14 days. Then, BC aqueous suspension was added to kraft pulp aqueous suspension. The content of BC that was added to the pulp suspension was as follows: 5, 10 and 15%. The disintegrated BC was turned into handsheets by a vacuum method. Dried handsheets were immersed in phenolic resin. To obtain composites, 5 immersed handsheets from each treatment were laid-up and hot pressed at 150 °C under 100 MPa pressure for 10 min. The specimens were characterized by means of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermal mechanical analysis (TMA), field-emission scanning electron microscopy (FE-SEM) techniques and insulating tests as dielectric loss factor and breakdown voltage. The results of thermal analysis showed an improvement in the thermal stability and an increase in the evaporation enthalpy of prepared samples with higher BC content. The mechanical examinations indicated that by increasing BC content in nanocomposites, the loss modulus and tan delta increased and the storage modulus of specimens decreased. The coefficient of thermal expansion (CTE) of samples diminished with increase of BC content. FE-SEM characterization showed different qualities of resin impregnation of the papers. The results of insulating tests confirmed that dielectric loss tangent and dielectric breakdown voltage increased in the specimens with higher BC content.

Phenolic resin-derived activated carbon-supported divalent metal as efficient adsorbents (M-C, M=Zn, Ni, or Cu) for dibenzothiophene removal

The adsorption process and mechanism of dibenzothiophene (DBT) over metal-loaded phenolic resin-derived activated carbon (PR-AC) were firstly reported in this work. The metal component (Zn, Ni, or Cu) was respectively introduced to PR-AC support via an impregnation method. The effects of adsorbent component, initial DBT concentration, liquid hourly space velocity (LHSV), adsorption time, and adsorption temperature on the adsorption capacity of the adsorbents were systematically investigated. Furthermore, the adsorption mechanism was discussed by analyzing the properties of adsorption product and saturated adsorbent as well as adsorption kinetics. Experimental results indicate that the PR-AC-loaded metal adsorbents, especially with Zn, present much higher DBT adsorption capability than that of pure PR-AC support. The DBT removal rate over PR-AC-loaded Zn (Zn²⁺ = 0.2 mol L^-1) reaches 89.14 %, which is almost twice higher than that of pure PR-AC (45.6 %). This is due to the π-complexation between DBT and metal ions (dominating factor) and the weakening of the local hard acid sites over PR-AC. The multi-factor orthogonal experiment shows that the DBT removal rate over PR-AC-loaded Zn sample achieved 92.36 % in optimum conditions.

High Surface-Enhanced Raman Scattering (SERS) Amplification Factor Obtained with Silver Printed Circuit Boards and the Influence of Phenolic Resins for the Characterization of the Pesticide Thiram

In this work, low-cost substrates with rough silver surfaces were prepared from commercial copper foil-covered phenolic board (CPB) and an aqueous solution of AgNO3, and were used for surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) measurements. A maximum SERS amplification factor of 1.2 × 10(7) was obtained for Rhodamine 6G (R6G), and use of the CPB resulted in a detection limit for Thiram pesticide of 0.5 µmol L(-1) The minimum detection level was limited by residual traces of phenolic groups that originated from the substrate resin, which became solubilized in the aqueous Ag(+) solution. It was found that the bands corresponding to the impurities had less influence in the Thiram analysis, which could be explained by the high affinity of sulfur for Ag surfaces. The influence of impurities in the SERS analyses therefore depended on the linkage between the rough silver surface and the analyte. The findings demonstrated the ease and effectiveness of using CPB to prepare a nanostructured surface for SERS.

Crossing the Traditional Boundaries: Salen-Based Schiff Bases for Thermal Protective Applications

A broad spectrum of applications of "Salen"-based Schiff bases tagged them as versatile multifunctional materials. However, their applicability is often bounded by a temperature threshold and, thus, they have rarely been used for high temperature applications. Our investigation of a classical Schiff base, N,N'-bis(4-hydroxysalicylidene)ethylenediamine (L2), reveals that it displays an intriguingly combative response to an elevated temperature/fire scenario. L2 resists and regulates thermal degradation by forming an ablative surface, and acts as a thermal shield. A polycondensation via covalent cross-linking, which forms a hyperbranched cross-linked resin is found to constitute the origin of the ablative surface. This is a unique example of a resin formation produced with a Schiff base, that mimicks the operational strategy of a high-heat resistant phenolic resin. Further applicability of L2, as a flame retardant, was tested in an engineering polymer, polyamide-6. It was found that it reinforces the polymer against fire risks by the formation of an intumescent coating. This paves the way for a new strategic avenue in safeguarding polymeric materials toward fire risks. Further, this material represents a promising start for thermal protective applications.

Production, separation and applications of phenolic-rich bio-oil--a review

This paper provides an overview of current research trends in the production and separation of phenolic-rich bio-oils, as well as their applications. The first part of this paper highlights the strong dependency of the phenolic content of bio-oil on the kinds of biomass feedstock, reaction system, reaction conditions, and the type of catalysts used in their production. More recent separation technologies are also discussed in the second part of the paper. The final part of the paper deals with recent experimental results from applications of phenolic-rich bio-oils in the synthesis of phenolic resins. The paper suggests that the microwave-assisted pyrolysis of palm residues is a promising route for phenolic-rich bio-oil production, and that the use of supercritical CO2 and switchable hydrophilicity solvents during extraction, as well as molecular distillation techniques, can be applied to increase the recovery of phenolic compounds from bio-oils.

Production of bio-based phenolic resin and activated carbon from bio-oil and biochar derived from fast pyrolysis of palm kernel shells

A fraction of palm kernel shells (PKS) was pyrolyzed in a fluidized bed reactor. The experiments were performed in a temperature range of 479-555 °C to produce bio-oil, biochar, and gas. All the bio-oils were analyzed quantitatively and qualitatively by GC-FID and GC-MS. The maximum content of phenolic compounds in the bio-oil was 24.8 wt.% at ∼500 °C. The maximum phenol content in the bio-oil, as determined by the external standard method, was 8.1 wt.%. A bio-oil derived from the pyrolysis of PKS was used in the synthesis of phenolic resin, showing that the bio-oil could substitute for fossil phenol up to 25 wt.%. The biochar was activated using CO2 at a final activation temperature of 900 °C with different activation time (1-3 h) to produce activated carbon. Activated carbons produced were microporous, and the maximum surface area of the activated carbons produced was 807 m(2)/g.

Glucose oxidase adsorption performance of carbonaceous mesocellular foams prepared with different carbon sources

Several carbonaceous mesocellular foams (C-MCFs) were prepared with MCF-silica as template using the carbon precursors of sucrose, furfuryl alcohol and lab-made phenolic resin, and the corresponding C-MCFs were named as C-MCF-Suc, C-MCF-FA and C-MCF-PR, respectively. The results of SEM, transmission electron microscopy, N2 adsorption-desorption and energy-dispersive X-ray measurements indicated that the C-MCFs prepared from different carbon source appeared morphologically with different degree of order and different pore distribution. The C-MCF-FA exhibited the highest ordered structure and the smallest pore distribution among the foams. The optimum conditions for adsorption of C-MCFs on glucose oxidase (GOD) were also studied, and the maximum adsorbance was determined. The adsorption of GOD on C-MCF-FA was performed at different pH with different GOD concentrations. The maximum adsorption (423.3 mg g(-1)) was observed near the isoelectric point of the GOD (pI ≈ 5.0) with a GOD concentration of 6.0 mg mL(-1), suggesting that the GOD adsorption on C-MCFs might be affected strongly by the electric repulsion between the GOD molecules. Moreover, GOD adsorption performances on different C-MCFs revealed that both the pore size and the pore volume played important roles in the adsorption process, and the window size of C-MCFs dominated the residual immobilized amounts of GOD. Compared to the other two C-MCFs, the C-MCF-FA with a smaller window pore (10 nm) and higher volume (1.40 cm(3) g(-1)) exhibited the highest GOD adsorption and catalytic activity. Furthermore, the immobilized GOD exhibited improved thermal and storable stabilities. Thus the C-MCF-FA could be served as the prospective GOD carrier material used in enzymatic fuel cells.