Recent Developments in Synthesis and Photocatalytic Applications of Carbon Dots

The tunable photoluminescent and photocatalytic properties of carbon dots (CDs) via chemical surface modification have drawn increased attention to this emerging class of carbon nanomaterials. Herein, we summarize the advances in CD synthesis and modification, with a focus on surface functionalization, element doping, passivation, and nanocomposite formation with metal oxides, transition metal chalcogenides, or graphitic carbon nitrides. The effects of CD size and functionalization on photocatalytic properties are discussed, along with the photocatalytic applications of CDs in energy conversion, water splitting, hydrogen evolution, water treatment, and chemical degradation. In particular, the enzyme-mimetic and photodynamic applications of CDs for bio-related uses are thoroughly reviewed

Biobased Polystyrene Foam-like Material from Crosslinked Cassava Starch and Nanocellulose from Sugarcane Bagasse

This research aimed to study the effect of lignin, natural rubber latex (NRL), nanocellulose, and talc on production of biobased foam using cassava starch as matrix. Comparison study on lignin extraction from sugarcane bagasse (SCB) for different types of base (KOH and NaOH), concentration (10 %w/w and 40 %w/w), and temperatures (60 C for 3 h and 120 C for 1 h) was performed. The most suitable isolation condition giving the highest yield of lignin and lowest hemicellulose contamination was 40 %KOH at 120 oC for 1 h. A mechanical method was superior to a chemical method for cellulose size reduction owing to more appropriate size distribution and uniformity of nanocellulose. The most favorable proportion of foam contained 20% nanocellulose, 3% talc, 0.1% NRL, 38.5% water, and 76.9% crosslinked cassava starch. These conditions resulted in favorable flexural strength, modulus, and percentage of elongation, analogous to polystyrene foam. An appropriate amount of added lignin increased the elasticity of biofoam

IMPROVING ENZYMATIC SACCHARIFICATION OF SUGARCANE BAGASSE BY BIOLOGICAL/PHYSICO-CHEMICAL PRETREATMENT USING TRAMETES VERSICOLOR AND BACILLUS SP.

In this work, laccase biosynthesis of two microorganisms, Trametes versicolor TISTR 3224 and Bacillus sp. TISTR 908 isolated in Thailand, was investigated using sugarcane bagasse (SCB) as substrate. Two-stage biological/physico-chemical pretreatment of SCB on delignification and saccharification yield was studied. A two-level full factorial design was applied and 3 factors influencing delignification and saccharification processes of SCB were studied including C:N ratio (10:1 to 20:1), temperature (100 to 140°C), and alkali concentration (0 to 5% w/w NaOH). It was found that during biological pretreatment of SCB, a greater amount of laccase was produced from T. versicolor in the early stage of growth compared with Bacillus sp. Nitrogen supplement enhanced laccase biosynthesis of T. versicolor. By contrast, Bacillus sp. required a smaller amount of nitrogen source to produce laccase. Biological treated bagasse was subsequently subjected to a physico-chemical treatment. The results showed that the highest xylose and glucose yield of 51.97% w/w based on carbohydrate content was obtained from T. versicolor cultivation at a C:N ratio of 20:1, and consecutively treated in 5% w/w NaOH solution at 140°C for 1 h. Bacterial/alkali and alkali pretreatment yielded xylose and glucose in smaller degrees compared with fungal/alkali pretreatment. T. versicolor preferentially degraded lignin in sugarcane bagasse relative to cellulose and hemicelluloses constituents, while Bacillus sp. simultaneously attacked both lignin and carbohydrate moieties, as indicated by analysis of relative FT-IR intensities ratios of pretreated and untreated sugarcane bagasse

Structure of methanol sub-monolayer on functionalized graphite at temperatures below the triple point

Grand canonical simulations were carried out to determine the microscopic structures of the sub-monolayer of methanol on a graphite model with two hydroxyl groups attached to the basal plane. At temperatures below the triple point temperature of methanol (176 K), the adsorption isotherm exhibits four distinct transitions: (1) saturation of the OH groups, (2) formation of 2D ring clusters floating on the basal plane, (3) transition to 2D string clusters with one end attached to the OH groups, and (4) compaction of the 2D string clusters. The variation in the molecular distribution and orientation for these transitions is studied, and correlated with the changes in isosteric heat across these transitions. It is found that the ring-to-string transition occurs more readily at low temperatures, and that the hydrogen bond length (O⋯H) within a ring or a string is constant

Techno-Economic Analysis for Bioethanol Plant with Multi Lignocellulosic Feedstocks

Oil palm empty fruit bunch and trunk are classified as primary lignocellulosic residues from the palm oil industry. They are considered to be promising feedstocks for bioconversion into value-added products such as bioethanol. However,using these lignocellulosic materials to produce bioethanol remains a significant challenge for small and medium enterprises. Hence, techno-economic and sensitivity analyses of bioethanol plant simultaneously treating these materials were performed in this study. The information based on preliminary experimental data in batch operations wasemployed to develop a simulation of an industrial-scale semi-continuous production process. Calculations of mass balance, equipment sizes, and production cost estimation of the production plant of various capacities ranging from 10,000 L/day to 35,000 L/day were summarized. The result based on 20 years of operation indicated that the net present value of theplant of lower capacities was negative. However,thisvalue became positive when the plant operated with a higher capacity, 35,000 L/day.The highest ethanol yield, 294.84 LEtOH/tonfeedstock, was produced when the planttreated only an empty fruit bunch generating 8.94% internal rate of return and US$0.54 production cost per unit.Moreover, the higher oil palm trunk ratio in the feedstock, the lower ethanol yield contributing to the higher production cost per unit

Lignin-Derived Syringol and Acetosyringone from Palm Bunch Using Heterogeneous Oxidative Depolymerization over Mixed Metal Oxide Catalysts under Microwave Heating

Biomass valorization to building block chemicals in food and pharmaceutical industries has tremendously gained attention. To produce monophenolic compounds from palm empty fruit bunch (EFB), EFB was subjected to alkaline hydrothermal extraction using NaOH or K2CO3 as a promotor. Subsequently, EFB-derived lignin was subjected to an oxidative depolymerization using Cu(II) and Fe(III) mixed metal oxides catalyst supported on γ-Al2O3 or SiO2 as the catalyst in the presence of hydrogen peroxide. The highest percentage of total phenolic compounds of 63.87 wt% was obtained from microwave-induced oxidative degradation of K2CO3 extracted lignin catalyzed by Cu-Fe/SiO2 catalyst. Main products from the aforementioned condition included 27.29 wt% of 2,4-di-tert-butylphenol, 19.21 wt% of syringol, 9.36 wt% of acetosyringone, 3.69 wt% of acetovanillone, 2.16 wt% of syringaldehyde, and 2.16 wt% of vanillin. Although the total phenolic compound from Cu-Fe/Al2O3 catalyst was lower (49.52 wt%) compared with that from Cu-Fe/SiO2 catalyst (63.87 wt%), Cu-Fe/Al2O3 catalyst provided the greater selectivity of main two value-added products, syringol and acetosyrigone, at 54.64% and 23.65%, respectively (78.29% total selectivity of two products) from the NaOH extracted lignin. The findings suggested a promising method for syringol and acetosyringone production from the oxidative heterogeneous lignin depolymerization under low power intensity microwave heating within a short reaction time of 30 min

Scaling-up of carbon dots hydrothermal synthesis from sugars in a continuous flow microreactor system for biomedical application as <i>in vitro</i> antimicrobial drug nanocarrier.

Carbon dots (CDs) are a new class of nanomaterials exhibiting high biocompatibility, water solubility, functionality, and tunable fluorescence (FL) property. Due to the limitations of batch hydrothermal synthesis in terms of low CDs yield and long synthesis duration, this work aimed to increase its production capacity through a continuous flow reactor system. The influence of temperature and time was first studied in a batch reactor for glucose, xylose, sucrose and table sugar precursors. CDs synthesized from sucrose precursor exhibited the highest quantum yield (QY) (175.48%) and the average diameter less than 10 nm (~6.8 ± 1.1 nm) when synthesized at 220°C for 9 h. For a flow reactor system, the best condition for CDs production from sucrose was 1 mL min-1 flow rate at 280°C, and 0.2 MPa pressure yielding 53.03% QY and ~ 6.5 ± 0.6 nm average diameter (6.6 mg min-1 of CDs productivity). CDs were successfully used as ciprofloxacin (CP) nanocarrier for antimicrobial activity study. The cytotoxicity study showed that no effect of CDs on viability of L-929 fibroblast cells was detected until 1000 µg mL-1 CDs concentration. This finding demonstrates that CDs synthesized via a flow reactor system have a high zeta potential and suitable surface properties for nano-theranostic applications

Facile preparation of aqueous-soluble fluorescent polyethylene glycol functionalized carbon dots from palm waste by one-pot hydrothermal carbonization for colon cancer nanotheranostics

Carbon dots (CDs) are categorized as an emerging class of zero-dimension nanomaterials having high biocompatibility, photoluminescence, tunable surface, and hydrophilic property. CDs, therefore, are currently of interest for bio-imaging and nano-medicine applications. In this work, polyethylene glycol functionalized CDs (CD-PEG) were prepared from oil palm empty fruit bunch by a one-pot hydrothermal technique. PEG was chosen as a passivating agent for the enhancement of functionality and photoluminescence properties of CDs. To prepare the CDs-PEG, the effects of temperature, time, and concentration of PEG were investigated on the properties of CDs. The as-prepared CDs-PEG were characterized by several techniques including dynamic light scattering, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, fluorescence spectroscopy, Raman spectroscopy, Fourier-transform infrared spectroscopy and Thermogravimetric analysis. The as-prepared CDs under hydrothermal condition at 220 degrees C for 6 h had spherical morphology with an average diameter of 4.47 nm. Upon modification, CDs-PEG were photo-responsive with excellent photoluminescence property. The CDs-PEG was subsequently used as a drug carrier for doxorubicin [DOX] delivery to CaCo-2, colon cancer cells in vitro. DOX was successfully loaded onto CDs-PEG surface confirmed by FT-IR and Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometer (MALDI-TOF/MS) patterns. The selective treatment of CDs-PEG-DOX against the colorectal cancer cells, , relative to normal human fibroblast cells was succesfully demonstrated