Communications in Science and Technology 10.
209Ae217
COMMUNICATIONS IN
SCIENCE AND TECHNOLOGY
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Biochar supported photocatalyst .
angrove biochar-TiO.
for organic pollutants removal via synergetic adsorption-photocatalytic process Nadya Ummi Azizaha,c.
Dessy Ariyantia,b,c,*.
Dina Lesdantinaa,b,c.
Erwan Adi Saputrad.
Vimal Chandra Srivastavae Department of Chemical Engineering.
Faculty of Engineering.
Universitas Diponegoro.
Semarang 50275.
Indonesia SDGs Center.
Universitas Diponegoro.
Semarang 50275.
Indonesia Center of Advanced Materials for Sustainability.
Universitas Diponegoro.
Semarang 50275.
Indonesia Department of Chemical Engineering.
Faculty of Engineering.
Universitas Pembangunan Nasional AuVeteranAy.
Surabaya 61119.
Indonesia Department of Chemical Engineering.
Indian Institute of Technology Roorkee.
Roorkee.
Uttarakhand 247667.
India Article history:
Received: 18 December 2024 / Received in revised form: 19 June 2025 / Accepted: 22 June 2025 Abstract Access to clean water remains a global challenge, which is made worse by the contamination of chemical dyes.
The recent innovations of wastewater treatment have been introduced, such as combined biochar with TiO2 photocatalyst.
This study proposed to degrade mainly organic pollutants from dyed wastewater using adsorption-photocatalytic of biochar-supported photocatalyst TiO2 (BSP).
Mangroves were converted into biochar via hydrothermal carbonization process and combined with TiO2 by a sol-gel method.
The composite was then characterized by SEM-EDX.
FTIR, and XRD.
The degradation performance of the BSPs was optimized with the addition of Titanium (IV) Isopropoxide (TTIP) solution in biochar for 15-25 mL, solution photocatalyst dosage 0.
5Ae1 g/L, initial dyed water concentration at 10 ppm, pH 5.
2, and UV-irradiation time from 30 to 240 min in a photocatalytic reactor.
The phenomenon of organic pollutants removal was observed based upon the mechanism and dominance of the process and the degradation reaction rate of organic pollutants in dyed wastewater.
Methylene blue used as a model dye was degraded 100% through the adsorption-photocatalysis process using BSP.
The highest effective degradation performance was found in BSP 20 that had a functional group area of 4.
39923 mA/g, a catalyst loading of 0.
5 g/L, and the highest degradation rate at k = 0.
021 minAA.
subsequent development, the synergistic interaction between biochar and TiO2 presents a promising avenue for the development of advanced wastewater treatment systems targeting the removal of organic pollutants, particularly in textile industry.
Keywords: Mangrove biochar.
adsorption-photocatalysis synergy.
titanium dioxide.
wastewater treatment Introduction Global water demand is growing inversely the accessibility of drinkable water for humans.
As reported by World Wildlife Foundation, about one billion people worldwide struggle to access clean water .
Some studies reported that worldwide wastewater, including dyed wastewater, reaches nearly 380 billion cubic meters per year .
Wastewater generated by textile industries is characterized by dark color, high concentrations of aromatic pollutants, alkaline properties, and complex substances .
It is estimated that more than 10 Ae 40% of chemically reactive dyes are wasted during the textile manufacturing process .
, which poses potential risks to humans and other organisms.
Extensive treatment is deemed critical to be applied to wastewater and azo dyes to achieve environmental quality Various technologies .
such as ozone oxidation, * Corresponding author.
Email: dessy.
ariyanti@che.
https://doi.
org/10.
21924/cst.
ultrafiltration, adsorption, photocatalysis, coagulation, and flocculation have been applied to remove these organic Adsorption and photocatalysis, in this case, have been widely utilized in wastewater treatment.
however, both have their distinctive challenges.
Producing adsorbents such as activated carbon, zeolite, alumina, and silica is high-priced, thus encouraging the development of other economical alternative adsorbents such as biochar.
Biochar is a carbon-rich substance that has a broad superficial area and functional groups, high porosity .
, and aloft relative carbon content of 40-75% .
It can be produced from the thermal conversion process of animal and plant biomass .
, such as seaweed .
, waste ginkgo leaf .
, waste walnut shell .
, and palm kernel shell .
So far, there are only a few studies on biochar from mangrove plants.
Most of the C elements in mangroves are stored in the roots .
03 Ae 40.
89%), leaves .
25 Ae 41.
74%) .
, and twigs .
40 Ae 43.
05%) .
The organic carbon content in living mangrove roots .
87 A 1.
98%) is marginally greater than that of the dead ones .
65 A 1.
28%) .
This open access article is distributed under a Creative Commons Attribution (CC-BY) 4.
0 license Azizah et al.
/ Communications in Science and Technology 10.
209Ae217 In many cases.
TiO2 photocatalyst is also used due to its excellent ability to break down organic pollutants through the photocatalysis process .
However, because of its wide band gap (Eg = 3.
2 eV).
TiO2 is only activated using UV or near-UV light .
To improve its photocatalytic performance.
TiO2 can be combined with biochar as biochar-supported photocatalysts (BSP) .
that may .
enhanced photocatalytic performance compared to pure TiO2.
have a large and efficient electron storage capacity that supplies electrons to TiO2, and .
added CAeOAeTi linkages within the composite structure that reduces the semiconducting energy gap and broadens the adsorption range to decrease energy levels .
A recent study by Ulfa et .
explored various supports for TiO2 by synthesizing TiO2-impregnated mesoporous silica using a gelatinAeP123 biotemplating method in which the results showed methylene blue (MB) degradation up to 95%.
This suggests that combining TiO2 with structurally tailored supports significantly can improve their performance.
In this research, mangrove biomass was converted into biochar through the hydrothermal carbonization (HTC) process at an optimal temperature of 250AC, as supported by previous studies on the efficiency for heat generation .
Ae.
Mangrove biochar was incorporated with TiO2 through the solgel method.
Other methods have also been applied by other researchers, such as Yue et al.
, producing BSP from barley-straw using the ultrasound-assisted method to degrade methylene blue.
Shi et al.
synthesizing a BSP using the hydrogenation method from sugarcane bagasse, and Martins et .
converting paper into magnetic biochar to produce BSP through the solvothermal process for the degradation of Sulfadiazine (SDZ) and Oxolinic acid (OXA).
This study reported the synergetic effect of biochar and TiO2 photocatalyst through adsorption-photocatalysis experiments and physicochemical characterization.
The photodegradation was performed in the organic pollutant removal using methylene blue as a model dye solution under UV irradiation loaded with a fine BSP.
The mechanism of both solids was proposed based on the kinetics of methylene blue degradation.
This study also offers a theoretical encouragement for the synergistic interaction between mangrove biochar and TiO2 in the decay of organic contaminants.
Materials and Methods Materials preparation The biomass used was derived from mangrove plants, particularly twigs and roots, which were obtained from Tapak Mangrove Tourism Village.
Semarang.
Furthermore.
Titanium (IV) Isopropoxide (TTIP) was purchased from Qingdao CEMO Biotechnology Co.
Ltd.
TiO2 was synthesized from TTIP via a sol-gel process and other chemicals such as Ethanol.
HCl, and acetic acid were from Supelco Merck (Sigma-Aldric.
Synthesis of biochar Mangrove twigs and roots were grounded and filtered for a 100Ae150m particle size range.
Biochar was prepared by 5 grams of biomass with 65 ml of distilled water .
:10wt%) in a 100 ml Teflon-linked Autoclave.
The hydrothermal carbonization method was carried out at 250AC for 3 hours .
Afterward, the biochar was left for 24 hours at room temperature before being filtered off and washed using DI water.
The initial pH of biochar was about 5.
9 Ae 6.
Using acid treatment, the biochar was later rinsed with HCl 0.
until the pH of the biochar dropped 1-2 levels to increase the functional groups .
It was then placed in a vacuum oven at 110AC for 2 hours.
Synthesis of biochar-supported photocatalyst The sol-gel method was utilized to incorporate mangrove biochar with TiO2.
5 grams of biochar was dispersed in 60 ml of ethanol and agitated for 2 hours .
TTIP at 15 ml, 20 ml, and 25 ml was dropped into each experimental container.
After a 2 hour-stirring, 2.
5 ml of deionized water and acetic acid was added by drop.
The stirring continued for the next 2 hours until a gel was formed, which later on was left overnight.
The solid obtained was transferred to a binder oven set at 105AC for 1 hour and calcined at 500AC for another hour to generate TiO2 Characterization The surface morphology of the BSP was identified by means of scanning electron microscopy (SEM-EDX JEOL JSM-6510LA).
The crystallinity of pure TiO2, mangrove biochar, and BSP samples were analyzed by X-ray diffraction spectroscopy (XRD Bruker 8D Advanc.
, scanned at 2=10A80A.
Fourier Transform Infrared Spectroscopy (FTIR PerkinElmer UATR Spectrum Tw.
was used to analyze the functional group on the biochar and BSPs and the data were also analyzed with the help of Origin software to obtain the functional group area of each sample.
Furthermore.
UV-visible spectrophotometry (Double Beam Spectrophotometer UH5.
was in use to evaluate the degradation performance.
Effectiveness of adsorption and photocatalysis The effectiveness of the adsorption-photocatalytic activity of all BSPs was examined by the kinetics of methylene blue (MB) degradation.
The initial volume for methylene blue was determined to be 500 mL with a concentration of 10 ppm.
The concentration of MB at the beginning and fixed intervals of the process was measured by adsorption in a dark optical box and photocatalytic using UV-visible light irradiation.
The methylene blue solution and BSP sample were then mixed and stirred in each experiment with a magnetic stirrer and various catalyst dosages .
5, 0.
75, and 1 g/L).
The photocatalytic process was performed in a custom photocatalytic reactor incorporating a Philips UV sterilizer unit .
low rate 1 GPM.
power 6 W.
voltage 220 V) with the irradiation intensity of 3645mW/cm2.
A 20 ml sample was taken every 30 minutes and injected using a 0.
2m PVDF syringe filter.
UV-vis Spectrophotometer was used to investigate the concentration of Results and Discussion Characterization of materials The surface characteristics of the prepared samples, as Azizah et al.
/ Communications in Science and Technology 10.
209Ae217 visualized in Fig.
1, were examined using Scanning electron microscopy (SEM).
The SEM analysis of BSP samples confirmed the successful immobilization of TiO2 on the external surface of the biochar by the sol-gel method.
TiO2 nanocrystals were deposited on the biochar surface through reactions .
Hydrolysis O Ti Oe O Oe R H2 O IeO Ti Oe O Oe H R Oe O Oe H Condensation (Dehydratio.
O Ti Oe O Oe H O Ti Oe O Oe H IeO Ti Oe O Oe Ti O H2 O Condensation (Dealcoholatio.
O Ti Oe O Oe R O Ti Oe O Oe H IeO Ti Oe O Oe Ti O R Oe O Oe H Alcohol Exchange O Ti Oe O Oe R RA Oe O Oe H IeO Ti Oe O Oe RA R Oe O Oe H Calcination O Ti Oe O Oe R Ie O = Ti = O H2 O CO2 All BSP composites synthesized with various volumes of TTIP demonstrated discernible TiO2 aggregation on the biochar The SEM analysis revealed that increasing the TTIPto-biochar volume ratio led to a corresponding increase in particle size, likely due to the enhanced aggregation of TiO2 nanoparticles during the precipitation stage of the synthesis process as described in a prior study by Fazal et al.
TiO2 loading became a key factor affecting the adsorption efficiency of the composite as it altered its specific surface area, pore structure, and porosity .
In particular, the BSP-25 sample, synthesized with the highest TiO2 loading, displayed significantly altered surface characteristics, including a notable reduction in pore volume and surface porosity compared to BSP-15 and BSP-20.
These morphological changes are consistent with the observed adsorption performance, wherein BSP-25 exhibited a reduced degradation rate under dark conditions.
This observation is aligned with findings reported in previous studies by Thuan et .
and Liu et al.
This diminished activity is likely attributable to the extensive TiO2 agglomeration, which may have impeded access to the active adsorption sites on the biochar surface .
, thereby limiting its effectiveness.
Fig.
SEM image of .
Biochar.
BSP 15.
BSP 20.
BSP 25 FTIR spectrum, as shown in Fig.
2, had a similar pattern for biochar and BSP.
The wavenumber explained that the characteristic peaks in the range of 2885 to 3390 cmOe1 from all the analyzed materials showed different surfaces on OeOH groups, which were derived from cellulose, hemicellulose, and lignin contained in mangrove plants.
The decline observed in Ae OH band intensity was determined by multiple factors, notably the thermal decomposition of hemicellulose, which began to undergo hydrolysis at approximately 200AC .
, or the engaged biochar in a bond-breaking interaction with TiO2 .
Thus, the incorporation of TiO2 led to a reduction in the amount of surface hydroxyl groups.
All samples exhibited similar adsorption peak in the range of 1590 to 1616 cmOe1, describing the existence of C=C and C=O aromatic rings .
Additionally, the OeCH2 deformation vibration and COeO stretching vibration indicated that the biochar surface contained a wide variety of functional groups.
The adsorption peak corresponding to OOeO bond vibration observed in the range of 440 to 576 cmOe1 indicated the formation of peroxyl bonds on the biochar surface following the TiO2 loading .
As widely reported for TiO2, the band observed in all BSP samples at wavenumbers around 500 cmAA Azizah et al.
/ Communications in Science and Technology 10.
209Ae217 is generally associated to TiOeOOeTi and/or TiOeO stretching vibrations .
This indicated that TiO2 was successfully synthesized on the surface of Mangrove Biochar.
Table 1 presents the summary of the details of the functional group of the mangrove biochar and all BSP samples.
Fig.
FTIR spectra of biochar and BSP Table 1.
Functional group of biochar (BC) and BSP Wavenumber .
m ) Annotation BSP 15
BSP 20
BSP 25
O-Ti-O and Ti-O C-H bending from aromatic ring (C-O) stretching vibrations ester and aliphatic ether (C=O) stretching (C=C) and (C=O) stretching and bending vibrations (C-H) stretching compounds (CH3.
CH.
(O-H) stretching Fig.
3 depicts the XRD patterns of pristine TiO2 and BSP composites with an output regarding the crystal structure phase of the TiO2 material .
The presence of anatase-phase TiO2 was confirmed by diffraction peaks at 2 values of 4A, 38.
3A, 48.
1A, 53.
9A, and 62.
8A, which corresponded to the .
, .
, .
, .
, .
, and .
crystal planes, referenced in JCPDS No.
21-1272 .
A progressive increase in peak intensity from BSP 15 to BSP 25 indicated a higher degree of TiO2 crystallinity, as more TiO2 was incorporated into the composite.
The pronounced peak at 3A confirmed the dominance of the anatase phase, which was widely recognized for its effective photocatalytic performance.
This result suggested that rutile TiO2 was present only in negligible amounts, as indicated by a weak peak observed near 54.
Zheng et al.
reported that photocatalysts featuring both anatase and rutile phases were more effective.
In addition, no obvious diffraction peaks associated with the biochar component were observed, likely due to its disordered, amorphous structure or the overshadowing effect caused by the crystalline TiO2 signals .
This suggested that TiO2 nanoparticles were well-distributed and successfully anchored on the biochar surface.
Fig.
XRD pattern of BSP Azizah et al.
/ Communications in Science and Technology 10.
209Ae217 Adsorption and photocatalytic activity of BSP The degradation performance of methylene blue in dark conditions indicated that biochar had more adsorption capacity than other materials.
It had twice as much adsorption capability than BSPs.
As the adsorption mechanism of materials is determined by their functional groups .
, the experiment results showed that mangrove biochar had the largest functional group area (Fig.
, reaching 132.
7939 m2/g.
It was conformable to its adsorption capability.
The functional groups .
ydroxyl, carboxyl, carbonyl, and amin.
contained in biochar support the adsorption of organic molecules and enhance their affinity .
This adsorption pathway applies an electron donor/acceptor according to the irregular distribution of electrons among the functional group of the biochar and the organic material .
BSP 25 had the lowest adsorption capability of other The functional group area of each BSP (Fig.
was 60198 m2/g (BSP .
, 4.
41947 m2/g (BSP .
, and 4.
m2/g (BSP .
BSP proved a smaller functional group area compared to biochar because of the dispersion of TiO2 into the spongy structure of Biochar .
BSP 15 also had a different Ti-O peak at 440 to 576 cm-1 than other BSP but its functional group area was larger than that of BSP 20 and BSP 25.
This might be due to the clumping of TiO2 in the sample .
, which caused Ti-O in BSP 15 to be unequally distributed.
Based on the characterization results, the marked improvement in the degradation efficiency of organic pollutants in dyed wastewater by BSP can be primarily ascribed to the strong interfacial interaction between biochar (BC) and TiO2 within the composite structure.
Accordingly, a plausible mechanism underlying the photocatalytic adsorption and subsequent reduction of methylene blue (MB) under UV irradiation by BSP is proposed and illustrated in Fig.
The adsorption-photocatalytic mechanism of BSP occurs in stages:
biochar in the composite serves as an adsorbent for dye (MB).
Therefore, a large quantity of MB is adsorbed onto the .
over light illumination, electron-hole pairs .
-/h ) are produced inside TiO2 nanoparticles deposited on biochar that break the MB adsorbed on the surface of biochar.
Fig.
Functional group area of .
biochar and .
,c,.
BSPs As illustrated in the proposed mechanism (Fig.
, biochar serves as a porous carbonaceous support that enhances the surface area and provides abundant active sites .
for the initial adsorption of MB molecules from solution.
Under the UV irradiation.
TiO2 absorbs energy that excites electrons .
A) in the valence band (VB) into the conduction band (CB), resulting in the formation of positive holes .
A) in the VB.
The photogenerated electrons are capable of reducing oxygen (OCC) molecules to reactive oxygen species (ROS), such as superoxide radicals (AOCCA), while the holes can oxidize adsorbed MB or water molecules to form hydroxyl radicals (AOH), both of which are powerful oxidants that contribute to the breakdown of MB.
The absorbance obtained from UV-Vis analysis explained that the concentration of the MB dye solution significantly decreased when being degraded using BSP under UV Azizah et al.
/ Communications in Science and Technology 10.
209Ae217 irradiation conducted in 3 times replication.
The BSP-20 with a catalyst loading of 0.
5 g/L exhibited an impressive degradation capability on 100% MB dye removal within 150 minutes of UV irradiation.
suggested in Fig.
The photodegradation kinetics of MB were described by a first-order model, indicating a concentration-dependent reaction rate .
The direct relationship existed between the reaction rate and the residual MB concentration in the solution (C), which is mathematically expressed as follows:
ya ln ya = yco.
yc Fig.
Adsorption-photocatalytic mechanism of BSP in methylene blue Fig.
Proposed pathway of degraded MB UVAeVis spectrum analysis revealed a continuous decline in the absorption peak at OO664 nm, indicating the progressive destruction of the chromophoric structure of methylene blue.
The appearance of new absorbance features in the UV region (<300 n.
suggested the formation of lower molecular weight Based on these observations and supported by previous studies, a proposed degradation pathway involving demethylation, ring cleavage, and eventual mineralization is .
C is an organic concentration at a specific time.
C0 is the starting concentration, k is the kinetics reaction constant, and t is time.
Different samples were loaded in MB solution and BSP 20 resulted in the highest degradation kinetic constant with k = 021/min.
This result aligned with earlier findings by previous work by Guo et al.
that applied similar kinetic model to investigate the synergistic interaction between biochar and TiO2 in a composite derived from rice husk biomass and Tetra n butyl titanate (TNBT).
In their study, the BC-TiO2 composite achieved a kinetic rate constant of 3.
15 y 10AA minAA for the toluene degradation via a combined adsorptionAephotocatalysis The comparison highlighted the enhanced photocatalytic performance of BSP 20, likely attributed to improved interfacial contact and surface functionality within the composite system.
The degradation curves and kinetic constants of MB at various catalysts are presented in Fig.
7 and Fig.
8, respectively.
The photocatalysis phenomenon is a multiple process reinforced by several process parameters such as temperature, light intensity, pH, concentration of pollutant, and catalyst In typical experiments.
The degradation rate rises as the catalyst loading in the system increases .
because adding a catalyst enhances the number of -OH radicals produced.
addition, the surface area available increases for higher adsorption-degradation capabilities.
Nonetheless, there is a preferred catalyst concentration level for achieving photocatalysis under UV light.
This study observed that the opacity may increase above its limit, thereby reducing light penetration through the environment due to increased light scattering from catalyst particles .
However, the following equation assesses the efficiency () of the concentrations in the photocatalytic solution.
Fig.
Reduction of MB concentration in adsorption-photocatalysis process using BSP, adsorption using BC, and photocatalysis using TiO2 Azizah et al.
/ Communications in Science and Technology 10.
209Ae217 Acknowledgments The authors acknowledged the Directorate General of Higher Education.
Research and Technology.
Ministry of Education.
Culture.
Research and Technology.
Indonesia, for the financial support No: 449A-74/UN7.
D2/PP/VI/2023 as well as Diponegoro University World Class University Program 2024
References