Preparation Of Ldhs—carbon-based Quantum Dots Nanocomposites And Study On Their Adsorption And Catalytic Performance

Layered Double Hydroxides(LDHs)are important inorganic layered crystals with novel features,such as thermal stability,interlayer anion exchangeability,memory effect,etc.They have been widely used in the fields of adsorption,catalysis,medicine,etc.Carbon Dots(CDs)and Graphene Quantum Dots(GQDs)are members of Carbon-based quantum dots family.CDs are fluorescent carbon nanoparticle with size of less than 10 nm.They have stable optical properties,rich oxygen containing functional groups(-OH,-COOH,-C=O,etc.),easy preparation and surface passivation,high surface area,low toxicity,low cost,mild reaction conditions,etc.GQDs have larger surface area and better biocompatibility than CDs.CDs and GQDs exhibit excellent catalytic properties,which hold great prospect for the potential application of adsorption.Herein,the following three researches were conducted:(1)Preparation of LDHs-CDs nanocomposite and the adsorption toward anionic adsorbents(methyl blue)In aqueous solution,LDHs can be used as an adsorbent to capture series of anionic contaminants.But the hydrogen bonding between the hydroxyl groups of LDHs and nitrogen or oxygen-containing groups during the adsorption process is very limited.The adsorption sites for hydrogen bonds in LDHs need to be increased to obtain better adsorption effect.Surface passivated CDs contain abundant oxygen-containing functional groups and can form hydrogen bonds with target substances,resulting in good adsorption performance.However,due to the water-soluble nature of CDs,hydrogen bond is relatively weak,and carrier is necessary in practical applications.Thus LDHs and CDs are combined to improve the adsorption efficiency and become good alternative material for removal of various organic and inorganic pollutants.Based on the adsorption characteristics of LDHs and CDs,LDHs-CDs nanocomposites were successfully synthesized by using positively charged LDHs and surface-passivated CDs with abundant oxygen-containing functional groups through simple and environmentally friendly process.CDs could be effectively and dispersedly assembled on the surface of LDHs,and the introduction of CDs into the LDHs can donate abundant hydroxyl groups on the surface of LDHs nanocomposite,facilitating the formation of hydrogen bonding between CDs and methyl blue.The adsorptive capacity of LDHs-CDs was evaluated by using methyl blue as a model anionic dye.LDHs-CDs could maintain high adsorption efficiency for methyl blue(maximum adsorption is 185 mg/g)while pH was in the range of 6?10.The pseudo-second-order model can best describe the kinetic data for methyl blue adsorption on the surface of the LDHs-CDs,and Langmuir model is suitable for the adsorption isotherm of methyl blue on LDHs-CDs.(2)Preparation of DBS-LDHs-CDs and generation of hydroxyl radicals using DBS-LDHs-CDs as heterogeneous Fenton-like catalystCDs which have high electron-donating properties and similar peroxidase activity in the Fenton-like reaction were combined with LDHs to design high-activity heterogeneous Fenton-like catalyst suitable for the generation of hydroxyl radicals.The catalytic activity of LDHs-CDs nanocomposites is improved significantly,which promotes the catalytic decomposition of H2O2 and produces a large amount of hydroxyl radicals.DBS-LDHs-CDs nanocomposites were prepared by using LDHs as the catalyst carrier.DBS-LDHs-CDs nanocomposite can be used as efficient heterogeneous Fenton-like catalyst to promote the decomposition of H2O2 in the acidic environment,resulting in abundant hydroxyl radicals accompanied with strong chemiluminescence.Moreover,freshly prepared DBS-LDHs-CDs could promote the degradation of dodecylbenzene sulfonate(DBS)without any external energy.The DBS-LDHs-CDs with excellent heterogeneous Fenton-like catalytic properties have great potential in the treatment of non-biodegradable water pollutants.(3)Preparation of SDS-LDHs-GQDs nanocomposite and the adsorption to nonionic organic adsorbents(2,4,6-trichlorophenol)To further expand the range of adsorption applications of LDHs and CDs,and investigate their adsorption capacity for nonionic organic adsorbates,SDS-LDHs-GQDs nanocomposites were obtained through hydrothermal synthesis by introducing citrate and dodecyl sulfate(SDS)into the LDHs layers.GQDs confined to the two-dimensional hydrophobic space were obtained.The adsorption behavior of SDS-LDHs-GQDs toward typical nonionic organic adsorbent 2,4,6-trichlorophenol was studied and the excellent adsorption was exhibited.The Maximum adsorption efficiency of SDS-LDHs-GQDs on 2,4,6-trichlorophenol was 80%,which was much higher than those of LDHs-GQDs(15%)and SDS-LDHs(40%).The maximum adsorption capacity was 119 mg/g.The pseudo-second-order model can be employed to best describe the kinetic data for the adsorption.Langmuir model is suitable for the adsorption isotherm.The efficient adsorption of 2,4,6-trichlorophenol by SDS-LDHs-GQDs is synergistic from hydrogen bonding and ?-? interactions,as well as SDS and nonion hydrophobic interactions between adsorbates(2,4,6-trichlorophenol).This provides new option for the adsorption of nonionic organic molecules and guidance for the development of other LDHs composites and GQDs adsorbents.