Synthesis and characterization of carbon nitride with tunable properties for photocatalytic degradation of phenol

Carbon nitride (CN) has been regarded as a potential visible light photocatalyst due to its light absorption up to ca. 450 nm and possesses band gap energy (Eg) of ca. 2.7 eV. CN can be prepared by thermal polymerization method using carbon and nitrogen-rich compound as the precursor. However, most of the reported CNs were associated with a defect-rich and less-ordered structure as well as low surface area that could affect their performance. In this study, CNs of high surface area, improved structural order, low Eg and low electron charge transfer resistance (Rct) that are practicable for photocatalytic degradation of phenol under a wide range of sunlight irradiation have been successfully prepared. At the early stage, various salt melts of KCl-LiCl, KCl-NaCl, and KCl-ZnCl2 were used in order to induce the crystallinity of CN. Despite all the salt melts helped to improve the optical properties as revealed by diffuse reflectance ultraviolet-visible (DR UV-Vis) spectroscopy, only salt melts of KCl-LiCl could form crystalline CN as shown by X-ray diffraction (XRD) patterns with the formation of crystalline poly(triazine imide). The fluorescence and electrochemical impedance (EIS) spectroscopy confirmed that the higher crystallinity has suppressed the electron hole recombination and decreased the values of Rct. Improved photocatalytic degradation of phenol (24%), of ca. 2.5 times better than that of amorphous CN (10%), was achieved on crystalline sample of CN-KCl-LiCl. Besides, optimizations of synthesis parameters including amount of precursor, synthesis temperature, synthesis time and amount of salt melt were conducted. Current study revealed that increasing the amount of precursor from 1 g to 3 g led to the decrease in photocatalytic activity from 12% to 5% of phenol degradation. Increasing reaction temperature from 500?C to 550°C increased the photocatalytic activity from 7% to 24%. However, the photocatalytic activity decreased to 20% when the reaction temperature was increased to 600°C. In addition, short synthesis time (2 h) and long synthesis time (6 h) have led to the low photocatalytic activity with 17% and 20% of phenol degradation, respectively. Meanwhile, low (2.5 g) and high (7.5 g) amounts of salt melts showed low photocatalytic activities of 14% and 11%, respectively. The optimized conditions for the synthesis of CN with high crystalline phase were 2 g of precursor, reaction temperature of 550?C, reaction time of 4 h and 5 g of salt melts. By employing the optimized synthesis parameters, both amorphous and crystalline CN were prepared using melamine (Mel) as the precursor. The photocatalytic testing of the crystalline CN-Mel showed an improved activity of ca. 1.5 times higher (30%) compared to amorphous CN-Mel (19%). Further modification to increase the surface area was carried out by creating porous structure using Pluronic P123 (P123) surfactant. Increasing the mass ratio of P123 to precursor from 0.02 to 0.05 improved the photocatalytic activity from 20% to 46%, but decreased to 37% at the high mass ratio (0.1). The high photocatalytic activity was due to its high surface area (160 m2 g-1) and low Rct values (11.49 kO). In order to improve the light absorption, modification of porous crystalline CN with 2,4,6-triaminopyrimidine (TAP) was conducted. Low addition of TAP (0.02 mass ratio) has significantly improved the photocatalytic activity up to 60%. The high activity was mainly due to the combination of high surface area (137 m2 g-1), low Eg (2.62 eV) and low Rct (14.52 kO) value. However, increasing the mass ratio of TAP from 0.03 to 0.1 decreased the photocataytic activity from 53% to 19%. Overall, this study has demonstrated that CN with tunable properties improved photocatalytic degradation of phenol that was nearly three times higher than unmodified CN under visible light region

Synthesis of carbon nanotube-titanium dioxide photocatalysts via modified sol-gel method for removal of phenol

In the present study, a series of carbon nanotube-titanium dioxide (CNT-TiO2) has been successfully synthesized by a modified sol-gel method in the presence of acetyl acetone as the chelating ligand. X-ray diffraction (XRD), diffuse reflectance ultravioletvisible spectroscopy (DR UV-Vis), Fourier transforms infrared spectroscopy (FTIR) and scanning electron microscope (SEM) were used to investigate the structural, optical properties and morphology of the sample. XRD patterns demonstrated that the addition of CNT maintained the anatase phase of TiO2, while DR UV-Vis analysis showed the additional absorbance in the visible light region after addition of the CNT, suggesting the successful incorporation of CNT into TiO2. The SEM image revealed the unaffected morphology of TiO2 after addition of the CNT. The photocatalytic removal of phenol was carried out under UV light irradiation at room temperature for 24 hours. It was confirmed that all CNT-TiO2 series showed better adsorption and photocatalytic activity than the TiO2. The best photocatalyst was 5% CNT-TiO2 with 68% of phenol removal, while TiO2 showed only 17% phenol removal. Adsorption process was proposed to be one of the important factors for the high activity. It was concluded that the incorporation of CNT into TiO2 using the modified sol-gel method would be a good alternative method to prepare highly active carbon based-TiO2 photocatalysts

Assessment of Post-Traumatic Stress Disorders and its Associations with Suicidal Behaviour among Adults Following Movement Control Order During COVID-19 Pandemic in Malaysia

A rapid review of previous outbreaks shows that a quarantine policy had greater effects on one’s psychological state including post-traumatic stress disorder (PTSD), confusion and anger caused by various stressors. This study aimed to assess the levels of Post-Traumatic Stress Disorder (PTSD) and its associations with suicidal behavior among Malaysian adults following Movement Control Order (MCO) during the COVID-19 pandemic in Malaysia. This cross-sectional study was distributed using an online standardized questionnaire composed of three parts, the socio-demographic characteristics, PTSD assessment using PTSD Checklist for DSM-5 and the suicidal behavior assessment using Suicidal Behaviors Questionnaire-Revised (SBQ-R). Almost half of the respondents had high PTSD symptoms (41.7 %) and low PTSD was 58.3 % among Malaysian adults. Furthermore, 69.6 % of participants had no suicidal behavior but, 30.4 % from the participants has suicidal behavior. This study found single status with highest PTSD (83.3 %) and marital status had significant correlation with PTSD which p-value was < 0.05. Malay was high percentage in high PTSD (74.6 %) and significant correlation between race and PTSD (p < 0.05). Employment status also had significant correlation with PTSD with p-value was 0.002 and students was counted highest PTSD (65.7 %). This study identified some socio-demographic factors and suicidal behavior associated with PTSD among Malaysian adults, which may lay ground for further interventions

Synthesis of carbon modified titanium dioxide photocatalysts for removal of phenol

Titanium dioxide (TiO2) has been recognized as an excellent photocatalyst, but lack adsorption capability. One of the suitable approaches to solve the problem is to introduce carbon materials to TiO2, through a simple process and only involve low cost precursors. In this study, carbon modified TiO2 was synthesized by using modified sol-gel method in the presence of acetyl acetone as the chelating ligand. Two carbon precursors of dichloromethane and carbon nanotubes (CNT) were used and the samples were denoted as DCM-TiO2 and CNT-TiO2, respectively. X-ray diffraction patterns showed that the addition of dichloromethane induced the formation of rutile phase in TiO2, while addition of CNT maintains the anatase phase of TiO2. Scanning electron microscope and field emission scanning electron microscope revealed the unaffected morphology of TiO2 after addition of the carbon precursors. The presence of carbon species was confirmed by diffuse reflectance ultraviolet visible spectroscopy and elemental dispersive X-ray analysis especially on samples with high loading of carbon precursors. The photocatalytic removal of phenol was carried out under UV light irradiation at room temperature for 24 hours. It was confirmed that all DCM-TiO2 and CNT-TiO2 series showed better adsorption and photocatalytic activity than the TiO2. The best catalyst for each series, which were 3% DCM-TiO2 and 5% CNT-TiO2, gave 72% and 68% phenol removal, respectively, while TiO2 showed only 17% phenol removal. Adsorption was proposed to be the important factor for the high activity. Since 3% DCM-TiO2 showed slightly faster rate constant than the 5% CNT-TiO2, it was proposed that the use of dichloromethane as carbon precursor and modified sol-gel as the simple method would be an alternative good method to prepare highly active carbon modified TiO2 photocatalysts

Properties and photocatalytic behaviour of vanadia loaded titania supported on mcm-41 synthesized using different surfactants for degradation of methylene blue

An attempt has been carried out to prepare vanadia loaded TiO2 supported on MCM-41(V-TiO2/MCM-41) nanostructured photocatalysts using different surfactants. The surfactants used in the photocatalysts synthesis were dodecyl-trimethyl-ammonium bromide (DTAB), hexadecyl-trimethyl-ammonium bromide (CTAB) and octadecyl-trimethyl-ammonium bromide (STAB) which have varied carbon chains. The effect of crystallinity, surface area and porosity of the MCM-41 support on the physical-chemical properties of synthesized photocatalysts of vanadia loaded TiO2/MCM-41 and their photocatalytic performance were investigated. X-ray diffraction (XRD) patterns showed that the crystallinity of vanadia-TiO2/MCM-41 decreased with increasing of carbon-chain number of the surfactant used. Both surface area and pore volume of V-TiO2 increased significantly from 16.2 m2/g and 0.034 cm3/g to 864.3 m2/g and 0.618 cm3/g, respectively, after being loaded on MCM-41 support which was prepared using CTAB. It was demonstrated that all the V loaded TiO2/MCM-41 materials exhibited remarkable improvement in photocatalytic degradation of methylene blue (MB) under the irradiation of visible light as compared to that of bare TiO2 and V-TiO2. Among these materials, V-TiO2/MCM-41 which was synthesized using CTAB appeared to be the best photocatalyst with 57% of MB removal under visible light irradiation

Synthesis of highly active crystalline carbon nitride prepared in various salt melts for photocatalytic degradation of phenol

Crystallinity could have a decisive influence on photocatalytic performance. In this study, the synthesis of crystalline carbon nitride (CN) was studied via an ionic melt polycondensation of urea precursor in the presence of various salt melts, which were KCl-LiCl, KCl-NaCl, and KCl-ZnCl 2 . While all the salt melts helped to improve the optical properties of the CN, only KCl-LiCl salt melt could form crystalline CN as evidenced by its X-ray diffraction pattern. Furthermore, the specific surface area of CN (72 m 2 /g) was maintained when using KCl-LiCl (73 m 2 /g), but it was decreased in the presence of KCl-NaCl (22 m 2 /g) or KCl-ZnCl 2 (17 m 2 /g). The CN prepared without the salt melt only showed 10% phenol degradation under the light of a solar simulator, while the use of KCl-LiCl significantly improved the activity to 24%. On the other hand, the CN prepared in the presence of KCl-NaCl and KCl-ZnCl 2 gave phenol degradation of 14% and 7%, respectively. This work demonstrated that the crystallinity, improved absorption in the visible light region, and maintained large specific surface area of the CN were crucial to achieve the high activity

Optimized synthesis temperature and time to obtain crystalline carbon nitride with enhanced photocatalytic activity for phenol degradation

In this work, the crystalline carbon nitride photocatalysts were synthesized by an ionothermal technique with varied synthesis temperature of 500, 550, and 600 °C, and varied synthesis time of 2, 4, and 6 h. Fourier transform infrared spectra showed the successful formation of the prepared carbon nitrides from their characteristic vibration peaks. X-ray diffraction patterns suggested that the same phase of poly(triazine imide) and heptazine could be observed, but with different crystallinity. The optical properties showed that different temperatures and synthesis time resulted in the different band gap energy (2.72–3.02 eV) as well as the specific surface area (24–73 m2 g–1). The transmission electron microscopy image revealed that the crystalline carbon nitride has a near-hexagonal prismatic crystallite size of about 50 nm. Analysis by high-performance liquid chromatography showed that the best photocatalytic activity for phenol degradation under solar light simulator was obtained on the crystalline carbon nitride prepared at 550 °C for 4 h, which would be due to the high crystallinity, suitable low band gap energy (2.82 eV), and large specific surface area (73 m2 g–1). Controlling both the temperature and synthesis time is shown to be important to obtain the best physicochemical properties leading to high activity

Simple and low-cost preparation of carbon-coated titanium dioxide via hydrothermal method

In the present study, carbon-coated titanium oxide (C-TiO2) was synthesized by hydrothermal method using dichloromethane as the novel low-cost carbon source. XRD patterns revealed that after purification method, only diffraction peaks of anatase TiO2 can be observed. On the other hand, the formation of carbon can be suggested from DR UV-visible spectrum and SEM image, which showed the additional of absorption band in the visible region and the successful formation of carbon that grew both on the surface with a unique noodle-like structure and surroundings of the TiO2 with non-uniform bulk structure, respectively

Photocatalytic degradation of photosensitizing and non-photosensitizing dyes over chromium doped titania photocatalysts under visible light

A series of 0.5–4 mol% Cr-doped TiO2 photocatalysts were tested over photocatalytic degradation of photosensitizing (Methylene Blue) and non-photosensitizing (Congo Red) dyes under visible light irradiation. Presence of Cr dopant has induced anatase-rutile phase transition, leading to high rutile percentage of 45% in the material. Besides, the addition of Cr dopant has extended the absorption wavelength of TiO2 to visible light region. As evidenced from the fluorescence analysis, electron-hole recombination rate of Cr-doped TiO2 decreased with increasing of Cr dopant content up to 3 mol% in the materials. Despite using the same series of photocatalysts, the optimum amount of Cr dopant which gave the best photocatalytic activity was different: 1 mol% Cr-doped TiO2 and 3 mol% Cr-doped TiO2 were the best photocatalysts for photodegrading Methylene Blue and Congo Red, respectively. The results strongly suggested that the nature of targeted subtract in photocatalysis reaction affected the photocatalytic performance of the Cr-doped TiO2. Possible mechanisms for photocatalytic degradation of the two different dyes over the photocatalyst were presented

Molecular dynamics simulations reveal the inhibitory mechanism of Withanolide A against α-glucosidase and α-amylase

Diabetes mellitus (DM) is a global chronic disease characterized by hyperglycemia and insulin resistance. The unsavory severe gastrointestinal side-effects of synthetic drugs to regulate hyperglycemia have warranted the search for alternative treatments to inhibit the carbohydrate digestive enzymes (e.g. α-amylase and α-glucosidase). Certain phytochemicals recently captured the scientific community's attention as carbohydrate digestive enzyme inhibitors due to their low toxicity and high efficacy, specifically the Withanolides-loaded extract of Withania somnifera. That said, the present study evaluated in silico the efficacy of Withanolide A in targeting both α-amylase and α-glucosidase in comparison to the synthetic drug Acarbose. Protein-ligand interactions, binding affinity, and stability were characterized using pharmacological profiling, high-end molecular docking, and molecular-dynamic simulation. Withanolide A inhibited the activity of α-glucosidase and α-amylase better, exhibiting good pharmacokinetic properties, absorption, and metabolism. Also, Withanolide A was minimally toxic, with higher bioavailability. Interestingly, Withanolide A bonded well to the active site of α-amylase and α-glucosidase, yielding the lowest binding free energy of -82.144 ± 10.671 kcal/mol and -102.1043 ± 11.231 kcal/mol compared to the Acarbose-enzyme complexes (-63.220 ± 13.283 kcal/mol and -82.148 ± 10.671 kcal/mol). Hence, the findings supported the therapeutic potential of Withanolide A as α-amylase and α-glucosidase inhibitor for DM treatment.Communicated by Ramaswamy H. Sarma