The Study On Large-scale Preparation Of Biomass Carbon Dots And Their Composites Performance

Carbon dots（CDs）are a new type of carbon-based zero-dimensional material.Compared with heavy metal-based semiconductor quantum dots,CDs have drawn significant attention due to their easy synthesis,favorable biocompatibility,tunable photoluminescence,excellent stability,low toxicity,favourable electronic properties.CDs have been widely applied in biosensing,bioimaging and energy conversion/storage.In addition to the above-mentioned advantages,biomass carbon dots（BCDs）prepared by biomass as raw materials can not only effectively reduce production costs but also achieve efficient conversion of waste resources.However,the current research on BCDs mainly focuses on the bioimaging and biosensing,and largescale preparation of BCDs remains to be further studied.Compared with fossil energy,hydrogen has a wide source and high energy density,and it is a promising clean,efficient and sustainable alternative energy.However,in the realization of large-scale hydrogen-based energy economy,hydrogen production technology is still a limited step.This is because the noble metal catalysts are still the most efficient catalyst materials in electrocatalysis water splitting（HER）and chemical release from hydrogen-storage materials.Unfortunately,the widespread commercialization of noble metal catalysts is limited by the scarcity and high cost.In addition,during the preparation and long-term storage,metal nanoparticles（NPs）usually lose catalytic performance due to particle aggregation and surface oxidation.Therefore,it is of great significance to find an effective method to reduce catalyst cost while improving catalyst activity and stability for the development of hydrogen energy.Carbon-based nanomaterials are ideal materials for various catalytic systems due to their excellent physical and chemical properties,high electrical conductivity,large surface area,and chemical inertness.As a new star material of the carbon family,BCDs has the advantages of simple production process,and can be produced in an environmentally friendly,low-cost,and high-yield way.Furthermore,the abundant functional groups（-COOH,-OH,etc.）on the surfaces of BCDs can coordinate with metal ions with empty d orbitals to form a relatively stable BCDs-metal ion coordination composite.During the pyrolysis process,the metal NPs are restricted between the BCDs to form ultrafine nanocrystals with stable structures,which effectively prevents the agglomeration and growth of the NPs during the reaction.Based on the above,we focuse on the large-scale preparation of BCDs and the application of BCDs-metal hybrid materials in catalytic hydrogen production.The specific contents are as follows:1.We reported the preparation of two biomass carbon dots（p-BCDs and r-BCDs）by simple green hydrothermal reaction using avocado as carbon source.The morphology structure and optical properties were studied by Transmission electron microscopy（TEM）,X-ray powder diffraction（XRD）,Fourier transform infrared spectroscopy（FT-IR）,X-ray photoelectron spectroscopy（XPS）,Ultraviolet and visible spectrophotometry（UV-Vis）and photoluminescence（PL）.The effects of hydrothermal temperature and time on the fluorescence were explored.The as-prepared BCDs showed bright blue and blue-green fluorescence,size uniformity,and excellent solubility and stability,the surface was highly functionalized with oxygen rich groups as well as nitrogen.In addition,the p-BCDs exhibited excellent Fe³⁺ sensitivity and could be used as Fe³⁺ fluorescent probes.Both p-BCDs and r-BCDs could prepare LED with high color rendering index by combining with epoxy resin.2.We reported a facile,green,kilogram-scale synthesis of high quality BCDs derived from poplar leaves using a one-step hydrothermal method.Importantly,the throughput of BCDs was 1.4975 kg in one pot.The obtained BCDs showed excellent PL properties,high photostability,size uniformity,and low cytotoxicity.The surface of the as-prepared BCDs was highly functionalized with oxygen rich groups as well as nitrogen.Finally,the as-prepared BCDs were successfully applied to hydrogen evolution reaction（HER）,selective detection of Fe³⁺ and bioimaging.3.We prepared highly crystalline N-dopping BCDs using ginkgo leaves as the raw material employing a simple treatment.Then Ru@BCDs was fabricated through a sample pyrolysis method.The Ru NPs were restricted between the BCDs to form ultrafine nanocrystals with stable structures,which effectively prevent the agglomeration and growth of the NPs during the reaction.The Ru@CQDs480 exhibited remarkable catalytic ability in 1 M KOH with an onset overpotential of 0 m V and it only required an overpotential of 10 m V to achieve the current density of 10 m A cm-2.It also exhibited excellent stability after 10 000 CV cycles.Density functional theory（DFT）calculations revealed a synergic effect between Ru NPs and CQDs that was responsible for the outstanding HER catalytic activity of Ru@CQDs.Most importantly,the cost of Ru@BCDs in this work was only 0.8 % of commercial Pt/C,which showed great application prospects.4.We reported N-dopping BCDs by hydrothermal method using tobacco as raw material,and then prepared Ru doped CoRu/BCDs hybrid material by hydrothermal and heat treatment methods.The the lattice strain of CoRu alloy was caused during the Ru doping,and the d-band energy and d-band center of Ru were changed,which greatly enhanced its electronic state density and catalytic activity.The electronic state density distribution,theoretically true atomic and molecular-level electronic structures were studied by X-ray absorption near-edge structure and density functional theory.The CoRu0.5/BCDs not only exhibited extraordinary catalytic activity for the hydrogen evolution reaction（HER）in 1 M KOH（j = 10 m A cm-2 at 18 m V and Tafel slope of 38.5 m V dec-1）,but also showed outstanding activity for chemical hydrogen generation from the hydrolysis of ammonia borane（AB）with a high turnover frequency（TOF）of 3255.4 mol H2 mol（Ru）-1 min-1 at 298 K.Furthermore,it showed excellent stability for both reactions.These benefits allowed this catalyst to be used for either reaction,thus greatly increased the efficiency of practical hydrogen production.