Ultrahydrophobic melamine sponge via interfacial modification with reduced graphene oxide/titanium dioxide nanocomposite and polydimethylsiloxane for oily wastewater treatment

Three-dimensional(3D)porous absorbents have attracted significant attention in the oily wastewater treatment technology due to their high porosity and elasticity.Given their amphiphilic surface,they have a propensity to simultaneously absorb water and oil,which restricts their range of applications.In this study,a reduced graphene oxide and titanium dioxide nanocomposite(rGO/TiO_(2))was used to fabricate an ultra-hydrophobic melamine sponge(MS)through interfacial modification using a solution immersion technique.To further modify it,poly-dimethylsiloxane(PDMS)was grafted onto its surface to establish stronger covalent bonds with the composite.The water contact angle of the sponge(rGO/TiO_(2)/PDMS/MS)was 164.2°,which satisfies the condition for ultrahydrophobicity.The evidence of its water repellency was demonstrated by the Cassie-Baxter theory and the lotus leaf effect.As a result of the increased density of rGO/TiO_(2)/PDMS/MS,it recorded an initial capacity that was 2 g/g lower than the raw MS for crude oil absorption.The raw MS retained 53% of its initial absorption capacity after 20 cycles of absorption,while rGO/TiO_(2)/PDMS/MS retained 97%,suggesting good recyclability.Excellent oil and organic solvent recovery(90%-96%)was demonstrated by rGO/TiO_(2)/PDMS/MS in oil-water combinations.In a continuous separation system,it achieved a remarkable separation efficiency of 2.4×10^(6)L/(m^(3)·h),and in turbulent emulsion separation,it achieved a demulsification efficiency of 90%-91%.This study provides a practical substitute for massive oil spill cleaning.

Characterization of Flame Retardancy and Oil-Water Separation Capacity of Superhydrophobic Silylated Melamine Sponges

A silylated melamine sponge(SMS)was prepared by two simple steps,namely,immersion and dehydration of a melamine sponge coated with methyltrichlorosilane.The silylated structure of SMS was characterized by FT-IR(Fourier-transform infrared)spectroscopy,SEM(Scanning electron microscopy)and in terms of water contact angles.Its oil-water absorption and separation capacities were measured by FT-IR and UV-visible spectrophoto-metry.The experimental results have shown that oligomeric silanol covalently bonds by Si-N onto the surface of melamine sponge skeletons.SMS has shown superhydrophobicity with a water contact angle exceeding 150°±1°,a better separation efficiency with regard to diesel oil(by 99.31%(wt/wt%)in oil-water mixture and even up to 99.99%(wt/wt%)for diesel oil in its saturated aqueous solution.Moreover,SMS inherited the intrinsicflame retardancy of the melamine sponge.In general,SMS has shown superhydrophobicity,high porosity,excellent selectivity,remarkable recyclability,and better absorption capacity for various oils and organic solvents,and a high separation efficiency for oil in saturated aqueous solutions.

Carbon materials from melamine sponges for supercapacitors and lithium battery electrode materials: A review

With the increasing energy demand together with the deteriorating environment and decreasing fossil fuel resources,the development of highly efficient energy conversion and storage devices is one of the key challenges of both fundamental and applied research in energy technology.Melamine sponges(MS)with low density,high nitrogen content,and high porosity have been used to design and obtain three‐dimensional porous carbon electrode materials.More importantly,they are inexpensive,environment‐friendly,and easy to synthesize.There have been many reports on the modification of carbonized MS and MS‐based composites for supercapacitor and lithium battery electrode materials.In this paper,recent studies on the fabrication of electrode materials using MS as raw materials have been mainly reviewed,including carbonation,doping activation,and composite modification of MS,and expectations for the development of porous carbon materials for energy storage as a reference with excellent performance,environment‐friendliness,and long life.

Joule-heated carbonized melamine sponge for high-speed absorption of viscous oil spills

Introducing heating function to oil sorbents opens up a new pathway to the fast cleanup of viscous crude oil spills in situ.The oil sorption speed increases with the rise of the temperature,thus oil sorbents with high heating temperature are desirable.Besides,the oil sorbents also need to be produced environment-friendly.Here we present carbonized melamine-formaldehyde sponges(CMSs)that exhibited superior heating performance and the CMSs could be massively fabricated through a non-polluting pyrolysis process.The conductive CMSs could be heated over 300℃with a low applied voltage of 6.9 V and keep above 250℃for 30 min in the air without obvious damage.Such high heating performance enabled heating up the oil spills with a high rate of 2.65℃·s^(-1) and 14%improvement of oil sorption coefficient compared with the state-of-the-art value.We demonstrated that one joule-heated CMS could continuously and selectively collect viscous oil spills(9,010 mPa·s)690 times its own weight in one hour.The CMSs will be a highly competitive sorbent material for the fast remediation of future crude oil spills.

A Facile and Green Construction of Biomimetic, Fluorine-free and Superhydrophobic Melamine Sponge with Magnetic-driven Function for Efficient Oil–water Separation and Oil Absorption

Inspired by nature,a superhydrophobic and magnetic melamine sponge(BFSM-MF)was fabricated by a one-step dip-coating method.Aiming at replacing nano-Fe_(3)O_(4) particles with a complex preparation process and high cost,the commercial and cheap Fe_(3)O_(4) originated from magnetite was employed as a magnetic substance.To acquire superhydrophobicity,the hierarchical mirco/nano-sized structure with low surface energy was mainly contributed by bonding hydrophobic Fe_(3)O_(4) and graphene with silicone resin onto the surface of the melamine sponge.The results demonstrated that the water and oil static contact angle values of BFSM-MF were 160°and 0°,revealing that BFSM-MF was superhydrophobic and super-oleophilic.Moreover,the self-cleaning ability,magnetic-driven oil absorption ability and continuous oil–water separation performance of BFSM-MF have also been evaluated.As expected,BFSM-MF possessed magnetic-driven oil absorption ability and the oil–water separation efficiency for light oil reaches 98%±1%.In addition,the adsorption capacity and recycling performance of diff erent organic solvents were systematically investigated.Therefore,the development of biomimetic,fluorine-free and superhydrophobic foam with magnetic-driven eff ect has potential application value in marine oil spill treatment and separation of domestic oil pollution.

Melamine sponge derived porous carbon monoliths with NiMn oxides for high performance supercapacitor

Supercapacitors with good electrochemical performance and flexibility are in great demand.In this paper,the concept of preparing 3D porous carbon monoliths via direct calcination of melamine sponge is presented.This preparation method is simple and has good control of the structure.Porous carbon composite nickel-manga nese oxides can be obtained by hydrothermal method followed with calcination.The electrochemical performances were tested and porous carbon monoliths with NiMn oxides exhibited a specific capacitance of 870 F/g in 1 mol/L KOH at a charge/discharge current density of 0.5 A/g and a capacity retention of 89.9% after 5000 times charge and discharge.

Experimental and Theoretical Study on Piezoresistive Behavior of Compressible Melamine Sponge Modified by Carbon-based Fillers

High-performance compression sensors have been playing an increasingly important role in human motion detection,health monitoring and human-machine interfaces over recent years.However,it remains a great challenge to develop theoretical models providing practical guidance to the sensor design.Herein,carbon black(CB),carbon nanotubes(CNTs)and graphene nanoplatelets(GNPs)were respectively incorporated into porous melamine sponges by a facile approach of dip-coating to fabricate compression sensors.Uniaxial compression-resistance tests show that the compressibility,stability and piezoresistive sensitivity of sensors could be tailored by the filler type and concentration.A model considering the number of conductive pathways(NCP)is given to describe the relationship between the resistance change and applied compression,showing extremely good agreement with the experimental data.Also,the correlation between the equivalent filler volume fraction and conductivity is described by the other two models proposed by McLachlan and Kirkpatrick,revealing the electrical percolation thresholds(Φc)for the conductive systems under compression.Among the three fillers,CB particles endowed the composite with the best piezoresistive sensitivity but the largestΦc due to its small size and aspect ratio.A combination of experimental study and theoretical model opens up a way of further understanding the piezoresistive sensing behavior as well as optimizing the electrical property and piezoresistivity of compressive conductive polymer composite.

Preparation and properties of a silver particle-coated and 1-dodecanethiol-modified superhydrophobic melamine sponge for oil/water separation

A Ag particle-coated and 1-dodecanethiolmodified melamine sponge(Ag-DDT-MS)was prepared through surface roughness by coating silver particles and subsequent grafting of a hydrophobic long hydrocarbon chain.Superhydrophobic and 3D porous Ag-DDT-MS was characterized by Fourier transform infrared spectroscopy,scanning electron microscope,energy-dispersive X-ray spectroscopy,and X-ray diffraction.The water contact angle of Ag-DDT-MS reached 159.2°.Ag-DDT-MS exhibited excellent absorption capacity for high viscous oils and organic solvents,ranging from 42.8 to 105.2 g∙g−1.The absorbed oils can be easily collected by the mechanical pressing process,and the oil recovery rate was satisfactory,more than 90%after 20 recycles.Ag-DDT-MS material also demonstrated good stability and excellent compressionrecovery ability,keeping 88.6%of the initial height after ten compression-release cycles.

Three-dimensional melamine sponge loaded with Au/ceria nanowires for continuous reduction of p-nitrophenol in a consecutive flow system

Herein, we report a versatile strategy to fabri- cate three-dimensional melamine sponge （MS）-Au/ceria nanowire （NW） networks to realize in situ continuous reduction of p-nitrophenol in a consecutive flow system. This system has proven to be high activity and stability. The ceria NW networks with large surface area can stabi- lize tiny Au nanoparticles dispersed on the ceria NWs, which are loaded on the framework of MS by dip-coating, and enhance the synergistic effect between ceria NWs networks and Au nanoparticles, leading to extremely high activity and good stability for catalytic application. The low-cost raw materials and catalyst with high activity and stability may make this three-dimensional MS-Au/ceria NWs composite material promising for continuous cat- alytic reaction application in industry or other fields.

Preparation of Three-dimensional Graphene-based Sponge as Photo-thermal Conversion Material to Desalinate Seawater

Water shortage has become one of the major threats to human society over the past centuries.The new interfacial solar evaporation is undoubtedly an attracting technology to solve this problem.Herein,graphene aerogel(GA)and graphene oxide/melamine sponge composite material(GO-MS)were prepared through a two-step reduction and one-step freezing method as photo-thermal materials to evaporate pure water and seawater.The proper concentrations of the graphene oxide(GO)dispersion for their preparation were investigated,which is 7 mg/mL for GA,and 5 mg/mL for GO-MS.The evaporation rates of GA are 1.40 kg/(m^(2)·h)for pure water and 1.21 kg/(m^(2)·h)for seawater,while for GO-MS it is 1.63 kg/(m^(2)·h)for pure water and 1.45 kg/(m^(2)·h)for seawater,respectively.The composite material not only reduces the usage of GO,but also shows better photo-thermal conversion properties.Furthermore,the heat loss of evaporation system was calculated and the method of further enhancing photo-thermal conversion efficiency was deduced,which will provide a strong basis for guiding the design and development of graphene based three-dimensional materials and further exploration in this field.

MOF‐derived 1D/3D N‐doped porous carbon for spatially confined electrochemical CO_(2) reduction to adjustable syngas

Electrochemical reduction of CO_(2) to syngas(CO and H_(2))offers an efficient way to mitigate carbon emissions and store intermittent renewable energy in chemicals.Herein,the hierarchical one‐dimensional/three‐dimensional nitrogen‐doped porous carbon(1D/3D NPC)is prepared by carbonizing the composite of Zn‐MOF‐74 crystals in situ grown on a commercial melamine sponge(MS),for electrochemical CO_(2) reduction reaction(CO_(2)RR).The 1D/3D NPC exhibits a high CO/H_(2) ratio(5.06)and CO yield(31 mmol g^(−1)h^(−1))at−0.55 V,which are 13.7 times and 21.4 times those of 1D porous carbon(derived from Zn‐MOF‐74)and N‐doped carbon(carbonized by MS),respectively.This is attributed to the unique spatial environment of 1D/3D NPC,which increases the adsorption capacity of CO_(2) and promotes electron transfer from the 3D N‐doped carbon framework to 1D carbon,improving the reaction kinetics of CO_(2)RR.Experimental results and charge density difference plots indicate that the active site of CO_(2)RR is the positively charged carbon atom adjacent to graphitic N on 1D carbon and the active site of HER is the pyridinic N on 1D carbon.The presence of pyridinic N and pyrrolic N reduces the number of electron transfer,decreasing the reaction kinetics and the activity of CO_(2)RR.The CO/H_(2) ratio is related to the distribution of N species and the specific surface area,which are determined by the degree of spatial confinement effect.The CO/H_(2) ratios can be regulated by adjusting the carbonization temperature to adjust the degree of spatial confinement effect.Given the low cost of feedstock and easy strategy,1D/3D NPC catalysts have great potential for industrial application.

Fabrication of BiOBr-silicone aerogel photocatalyst in an aqueous system with degradation performance by sol-gel method

It is a challenge to endow the material with the ability to pollutants degradation while maintaining the oil/water separation performance. Herein, the mixed dispersion of BiOBr photocatalyst and silicone sol was adsorbed in melamine foam. Superhydrophobic BiOBr-silicone aerogel(WCA=154°) was obtained through the transfer melamine foam to an autoclave and reaction at 80℃ for 20 h. The prepared superhydrophobic BiOBr-silicone aerogel can effectively remove the water soluble pollutants which remain within the water phase after oil/water separation. The band gap of the superhydrophobic BiOBr-silicone aerogel was calculated to be 2.71 eV, which shows sensitivity to visible light(458 nm). Through mechanism analysis, it is found that the VB position of BiOBr is at 1.07 eV and the position of CB is at-1.64 eV. Finally, we prepared a superhydrophobic BiOBr-silicone aerogel(5 cm×5 cm×3 cm) for the verification of the large scale preparation.

Efficiently photothermal conversion in a MnO_(x)-based monolithic photothermocatalyst for gaseous formaldehyde elimination

Volatile organic compound(VOC)pollution has a serious impact on human and urgently needs to be controlled through the development of new methods and catalytic materials.Compared with traditional thermal catalytic oxidation,the synergistic photothermocatalysis is regarded as a green and environmen-tally friendly strategy for organic compound pollutant removal,which can promote spontaneous heating of the surface of catalysts to achieve thermal catalytic reaction conditions via harvesting light irradia-tion.In this paper,a monolithic photothermocatalyst was synthesized through coating graphene oxide(GO)and MnOx in turn on a commercially available melamine sponge,where the GO mainly acted as a photothermal conversion layer to heat the catalytically active MnO_(x).This monolithic catalyst presented excellent photo-induced activity for formaldehyde elimination under ambient conditions(∼90%degrada-tion ratio in 20 min for∼160 ppm initial concentration formaldehyde),and meanwhile possessed a high catalytic durability for multiple cycles.The kinetic study demonstrated that this photothermocatalytic process followed a pseudo-second-order kinetics.Finally,we proposed a possible formaldehyde degrada-tion pathway based on in situ DRIFTS examination.