This study investigates the photocatalytic degradation of methylene blue (MB) using an Ag-Pterocarpus santilinoides extract biochar nanocomposites (AgPSBN) followed by characterization and antimicrobial screening of the biogenic photocatalyst. The silver biochar nanocomposite was synthesized by incorporating silver nanoparticles onto the surface of biochar through a facile, biogenic, safe, cost-effective and ecofriendly method. The photosynthesized AgPSBN was porous and spherical with a size of 27 nm range. The UV-spectroscopic analysis indicated spectra bands at 648 and 667 nm for biochar and nanocomposite, respectively. The low band gap energy of 2.0 and 1.8 eV for the biochar and nanocomposite, respectively, is an indication that they can be an effective photocatalyst for the degradation of MB and for other energy applications. The percentage removal efficiency of 96.33% indicates high photodegradation ability which remained fairly constant (75%) after five cycle reuse indicating stability of the nanocomposite. The rate constant was evaluated to be 0.008 min−1. The nanocomposite indicated high inhibition zone diameter for Salmonella, E. coli, Klebsiella, and Staphylococcus aureus with inhibition zone diameters of 15, 12, 10, and 8 mm, respectively. The results strongly suggest the nanocomposite to be an effective environmental decontaminant of dyes as well as microbes.

  • Ecofriendly silver@pterocarpus santilinoides biochar-organic–inorganic hybrid nanocomposites were fabricated.

  • Nanocomposite was crystalline, porous and spherical with a size of 27 nm range.

  • Photocatalytic study indicated a 96.33% decimation of MB.

  • Antimicrobial effectiveness shows high zones of microbial inhibition.

  • Reusability of the nanocomposite indicated 75% stability after five cycles.

Photocatalytic degradation is currently at the forefront of research as an advanced and environmentally friendly approach for the removal of organic pollutants from contaminated water and other matrixes. Among various photocatalysts, nanocomposites have gained significant attention due to their enhanced catalytic properties and synergistic effects (Mohammed et al. 2021; Balaji et al. 2023; Payel & Debajyoti 2023). One such promising nanocomposite is the silver biochar nanocomposite, which combines the photocatalytic activity of silver nanoparticles with the adsorption capacity of biochar. By combining the unique properties of silver nanoparticles (AgNPs) with Pterocarpus santilinoides leaves and biochar, a synergistic effect is achieved, leading to enhanced photocatalytic and antimicrobial capabilities (Nworie et al. 2023).

Methylene blue (MB) is a commonly used dye in industries such as textiles, printing, and paper production. However, its release into water bodies poses a severe threat to the environment and human health due to its toxicity and carcinogenic properties (Ahmed et al. 2023; Mustafa et al. 2023). Therefore, the development of efficient and cost-effective methods for its removal is of utmost importance.

P. santilinoides, commonly known as African padauk, is a tree species found in tropical regions. Pterocarpus is a genus of flowering plants in the family Fabaceae (legume family), and it includes several species, such as Pterocarpus santalinus (Indian redwood or red sandalwood) and Pterocarpus indicus (Amboyna wood). These species are known for their timber, medicinal properties, and cultural significance in various regions. Extracts from various parts of the plant, including the leaves, bark, and heartwood, are believed to have potential health benefits, such as anti-inflammatory, antioxidant, antimicrobial, and wound-healing properties (Ihedioha et al. 2019). Biochar, a carbon-rich material produced through the pyrolysis of biomass, has gained prominence as an ecofriendly and sustainable material. Biochar has a highly porous structure and high carbon content making it a good candidate for the sorption of contaminants and in inactivation of microorganisms (Abdelazeem et al. 2022).

Silver nanoparticles (AgNPs) possess unique optical, electrical, and catalytic properties, making them excellent candidates for photocatalytic applications and antimicrobial materials (Abdelazeem et al. 2022). Several studies have implicated silver nanoparticles to effectively generate reactive oxygen species (ROS) upon exposure to light, which can oxidize and degrade organic pollutants (Singh & Dhaliwal 2020). However, the aggregation and limited stability of AgNPs restrict their practical application. To overcome these limitations, researchers have incorporated AgNPs into biochar, a carbonaceous material derived from biomass pyrolysis. Biochar possesses a high surface area, porous structure, and strong adsorption capacity, which can immobilize AgNPs, facilitate the photocatalytic degradation process and enhance antimicrobial properties (Abdelazeem et al. 2022; Nworie et al. 2023). The combination of silver, biochar, and leaf extract creates a powerful composite material with enhanced photocatalytic and antimicrobial activity. The resulting silver biochar nanocomposite combines the advantages of both materials (silver nanoparticle and biochar), leading to improved stability, increased catalytic efficiency, increased antimicrobial potency, and enhanced dye adsorption capacity. The incorporation of silver nanoparticles into biochar matrices offers several advantages. Firstly, the biochar acts as a stabilizing agent for the silver nanoparticles, preventing their aggregation and ensuring a sustained release of silver ions over time. This sustained release is crucial for long-lasting antimicrobial effects, a quality currently sought in drug industries. Secondly, biochar provides a stable and environmentally friendly support material for silver nanoparticles, allowing their application in various fields, including water treatment, health care, food packaging, wound healing, environmental remediation, and agriculture (Mohammed et al. 2021; Balaji et al. 2023). In the healthcare sector, these nanocomposites can be used in wound dressings, medical devices, and coatings to prevent infections and promote faster healing. In environmental applications, they can be employed for water purification and filtration, effectively removing harmful bacteria and pathogens (Abdelazeem et al. 2022). Additionally, incorporating silver biochar nanocomposites into food packaging materials can extend the shelf life of perishable products by inhibiting the growth of spoilage microorganisms.

Silver biochar nanocomposites have gained significant attention in recent years due to their remarkable antimicrobial properties. The antimicrobial activities of silver biochar nanocomposites arise from the synergistic effects of silver nanoparticles and the porous structure of biochar (Abdelazeem et al. 2022). Silver nanoparticles exhibit excellent antimicrobial properties by releasing silver ions, which have the ability to disrupt bacterial cell membranes and inhibit the growth of a wide range of microorganisms. Biochar, on the other hand, provides a high surface area and a porous structure that enhances the contact between the nanocomposites and microorganisms, facilitating antimicrobial action. The antimicrobial activities of silver biochar nanocomposites have been extensively studied against a wide range of microorganisms, including bacteria, fungi, and viruses (Abdelazeem et al. 2022). Numerous studies have reported the effective inhibition and killing of pathogenic bacteria such as Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Salmonella spp (Abdelazeem et al. 2022). The nanocomposites have also demonstrated strong antifungal properties against species such as Candida albicans and Aspergillus niger (Abdelazeem et al. 2022). Moreover, recent research has explored the antiviral potential of silver biochar nanocomposites, showing promising results in inhibiting the replication of viruses like influenza and herpes simplex (Akbarzadeh et al. 2018).

In this study, the synthesis of the nanocomposite, structural and morphological properties, photocatalytic performance and antimicrobial properties were evaluated. The effects of various parameters, such as catalyst time of contact and initial dye concentration, were systematically studied to optimize the degradation efficiency.

Instrumentation

The UV-Vis spectra were obtained using a Genesis 10S UV-Vis spectrophotometer. A Bruker® D8 Discover x-ray diffractometer, equipped with a Lynx Eye detector, under Cu-Ka radiation (λ = 1.5406 Å) radiation at 40 kV and at 30 mA) was used for the determination of the crystalline nature of the biochar and nanocomposite and diffraction recorded with 2θ = 10 to 70. Phenomprox by Phenom World Eindhoven, Netherlands was used to determine the structural morphology and elemental composition of the nanocomposite and biochar (SEM/EDX analysis). A Cary 630 Agilent Technologies, USA Fourier transform infrared spectrophotometer (Shimadzu, Japan) in the range of 4,000–400 cm−1 in KBr using nujol mull as the mulling agent was used for functional group determination. All drying and shakings were effected using oven (model DHG) rotary shaker (RF-12 Remi equipment), respectively. Autoclave (Alpha Laboratory, Ltd) model NL280-A, Pressure Cooker (Crown Star Atsago, India Instruments Pvt Ltd, India and water bath (helmreasinn multipurpose) model: DK420 were used for the antimicrobial experiment.

Reagents

The following analytical grade reagents were obtained from Merck Germany and used without further purification; nitric acid (HNO3), MB dye, sodium hydroxides (NaOH), aqueous ammonia (NH3), dimethylsulfoxide, and hydrochloric acid (HCl). Nutrient broth and Mueller Hinton agar were sourced from TM-media laboratory PVT ltd.

Preparation of P. santalinoides leaf extract

P. santalinoides leaves were washed, dried for 7 days under the sun and ground into powder. Exactly 5 g of the powdered leaves were dissolved in 100 cm3 of distilled water and then heated with stirring at 80 °C for 30 min. The solution was then filtered and the filtrate was kept at 4 °C for further use.

Preparation of P. santalinoides leaf biochar

The P. santilinoides leaves were collected, cleaned, washed severally with deionized water and dried under the sun for 7 days. The dried leaves were then kept at a temperature of 60 °C for 3 h in an oven. The oven-dried leaves (500 g) were carbonized in an N2 environment at the temperature of 500 °C for 2 h. The carbonized biochar product was then ground into fine powder and kept for further analysis in an airtight container.

Synthesis of Ag-P. santilinoides extract biochar nanocomposites (AgPSBN)

Exactly 0.79 g of pulverized P. santilinoides biochar was added to 100 cm3 of distilled water, followed by the addition of 0.015 g of AgNO3 to the biochar dispersion and the mixture shaken vigorously for 30 min. Thereafter 10 cm3 of P. santilinoides extract was added to the solution, stirred and heated at 80 °C to reduce the silver ions on the surface of the biochar. The nanocomposite formed was separated by centrifugation, washed three times with distilled water and ethanol and then dried in an oven at 60 °C for 24 h.

Photocatalytic degradation of MB under different concentrations

Exactly 5 mg (0.005 g) of the nanocomposite was added to 10 cm3 of three different concentrations of MB solution (10, 25 and 50 ppm). The control was executed using 5 mg of biochar with MB of 25 ppm concentration. The extraction bottles were four and contained (i) 5 mg of biochar and 10 cm3 of 25 ppm MB (ii) 5 mg nanocomposite, 10 cm3 of 10 ppm MB (iii) 5 mg nanocomposite 10 cm3 of 25 ppm MB (iv) 5 mg nanocomposite, 10 cm3 of 50 ppm MB. The preparation, mixing, and shaking or equilibration was under dark conditions for 30 min. The solution was stirred under sunlight as a visible light source and monitored for 20 min. Then 2 cm3 aliquots from each extraction bottle were removed and centrifuged at 17,000 rpm for 2 min to separate solid nanocomposite. The absorbance of the supernatant of MB dye in all the samples was measured at 640 nm in a UV-Vis spectrophotometer using a quartz cuvette. The percentage of MB degradation was evaluated using the following equation:
(1)
where Ao is the absorbance of control, and A is the absorbance of solution.

Variation of time of photocatalytic activity (kinetic studies)

The effect of time on the photocatalytic degradation of MB was executed using five separate extraction bottles. Exactly 5 mg (0.005 g) of nanocomposite and 10 cm3 of 25 ppm of MB in five separate extraction bottles were prepared in the dark and allowed to equilibrate for 30 min. The different extraction bottles labeled A to E were allowed under the sunlight and removed at intervals of 20, 40, 60, 80, and 100 min, respectively. Thereafter, 2 cm3 of the aliquots were removed and centrifuged at 17,000 rpm for 2 min and the absorbance of the supernatant MB was measured at 640 nm in a quartz cuvette.

The percentage of MB degraded was evaluated using the following equation:
(2)
where Ao is the absorbance of control and A is the absorbance at time, t.

Desorption of MB from nanocomposite and reusability

Exactly 10 cm3 of different concentrations ranging from 0.10 to 0.001 M of HCl was added into three different extraction bottles containing 0.05 g of nanocomposites obtained after the photocatalytic experiment. The three sample bottles were agitated for 30 min, then filtered and the UV of the supernatant was taken at 640 nm against blank. The recovered nanocomposite was dried and reused for the removal of MB. This was repeated five times and the UV at each cycle extraction was recorded at 640 nm against blank.

Antimicrobial screening of the biochar and nanocomposite

Organisms studied are biologically relevant in clinical fields and include S. aureus, Salmonella sp., Klebsiella, and Escherichia coli. The clinical isolates were sourced from the Federal Teaching Hospital, Abakaliki, Nigeria and transported using nutrient broth to the ultra-modern laboratory of the Department of Applied Microbiology, Ebonyi State University, Abakaliki. The antimicrobial inhibitory test was performed on the biochar and nanocomposites against the test organisms S. aureus, Salmonella sp, Klebsiella and Escherichia coli as described elsewhere with little modifications of first dissolving the biochar and nanocomposites in dimethylsulfoxide (Nworie et al. 2018; Mohammed et al. 2021; Balaji et al. 2023). The culture of the test organisms was made in nutrient broth, incubated for 24 h and adjusted to the MCFarland turbidity standard. Blanks which act as control were prepared from a single antibiotic disc impregnated with ampiclox aseptically deposited on the Mueller Hinton agar plates. The culture of the test organisms and control were incubated at 370 °C for 18–24 h. The inhibition zone diameter was evaluated.

The FTIR spectra of P. saintilinoides leaf biochar, the nanocomposite and MB-loaded nanocomposite are shown in Figure 1(a)–(c). Characteristic vibrational peaks emerged at 3,283.1, 3,213.9, and 3,239.2 cm−1 for the –OH of biochar, Ag nanocomposite, and MB-loaded nanocomposite, respectively. This could be due to intra- and intermolecular hydrogen bonding common in polymeric species (Tank et al. 2024). The difference in spectra between the biochar and Ag nanocomposite and between the Ag nanocomposite and MB-loaded Ag nanocomposite was 69.2 and 25.3 cm−1, respectively, an indication of complexation interaction between the biochar and Ag nanocomposite. The vibration was observed at 1,900 1cm−1 for the biochar shifted to 1982.9 cm−1 for the Ag nanocomposite. This stretching was assigned to C = O of the P. saintilinoides biochar and indicates free electron conjugation of P. saintalinoides (Aayush et al. 2024). The difference in spectra between the biochar and Ag nanocomposite was 82.9 cm−1 illustrating a strong complexation interaction between the biochar, silver, and the extract. The band observed at 1,379.4 cm−1 for biochar shifted to 1315.8 cm−1 for the Ag nanocomposite and then to 1,375.4 cm−1 for MB-loaded Ag nanocomposite and was due to C–N symmetrical stretching vibration. The vibration band observed at 1,021.0, 1,032.0 and 1,110.7 cm−1 for the biochar, Ag nanocomposite and MB-loaded nanocomposite, respectively, was characteristic of unpyrolyzed ether functionalities (C–O–C) present in cellulose and hemicelluloses according to previous reports (Nima et al. 2024; Suresh et al. 2024). The intense band observed at 693.3, 779.0, and 779.0 cm−1 for the biochar, Ag nanocomposite, and MB-loaded nanocomposite, respectively, was assigned to the ester vibration of monosubstituted aromatic rings (Zakarya et al. 2024).
Figure 1

(a) Fourier infrared (FTIR) spectroscopy analysis of Pterocarpus santanoloides biochar. (b) Fourier infrared (FTIR) spectroscopy analysis of nanocomposite. (c) Fourier infrared (FTIR) spectroscopy analysis of MB nanocomposite.

Figure 1

(a) Fourier infrared (FTIR) spectroscopy analysis of Pterocarpus santanoloides biochar. (b) Fourier infrared (FTIR) spectroscopy analysis of nanocomposite. (c) Fourier infrared (FTIR) spectroscopy analysis of MB nanocomposite.

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UV-visible spectroscopy

The successful formation of nanoparticles, an indication of the bioreduction of metal salts, can efficiently be determined by the use of UV-visible spectroscopy. The determined surface Plasmon resonance peak of the biochar and nanocomposite was observed at 648 and 667 nm (Figure 2(a) and (b)), respectively, which was within the ambient of other studies involving functionalized biochar (Singh & Dhaliwal 2020; Abdelazeem et al. 2022). Evaluating the band gap energy (Eg) of the biochar and nanocomposite using Tauc plot previously used by other researchers (Dibya & Hara 2023; Jitendra et al. 2023) and as illustrated in Figure 2(c) and (d) involves plotting of Kubelka–Munk function (αhv)2 against band gap energy (Eg = hv = hC˄) as shown in Equation (1) (while noting h as Planck constant, α as absorption coefficient, v as the frequency of radiation and c as the speed of light and K as energy independent constant). Careful extrapolation from the linear part of the energy plot indicated that the band gap energy of the biochar and nanocomposite are 2.00 and 1.80 eV, respectively. The band energy gap of the Ag nanocomposite was lower than that of the biochar as evaluated, indicating that the attachment of the Ag-plant extract nanoparticle to the biochar decreased the band energy gap and facilitated the creation of new energy states in the nanocomposites which invariably will lead to increased photocatalytic and antimicrobial activity. This observation is consistent with results obtained from similar studies involving photosynthesized nanocomposites (Abdelazeem et al. 2022)
(3)
Figure 2

UV-Visible spectroscopy of (a) biochar (b) nanocomposite. (c,d) Band gap energy of (c) biochar (d) nanocomposite.

Figure 2

UV-Visible spectroscopy of (a) biochar (b) nanocomposite. (c,d) Band gap energy of (c) biochar (d) nanocomposite.

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XRD of biochar and nanocomposite

The XRD analysis gives the crystal structure and lattice of the biochar and nanocomposite. Characteristic peaks were observed at 24.4°, 26.5°, and 28.5° (Figure 3(a)) for the biochar which was indexed to the (110), (011), and (002) planes, respectively, as ascribed by other researchers (Fong et al. 2020; Fikadu et al. 2023). For nanocomposite (Figure 3(b)), new peaks were observed at 32.1° and 40.6° indexed to (111) and (100) planes, respectively, and refers to face-centred cubic silver (JCPDS file number: 040783) as previously noted by other researchers for Ag-biochar composites. The emergence of the (111) plane is consistent with the preferred growth pattern of Ag-biochar nanocomposites photosynthetically fabricated according to previous studies (Fairuzi et al. 2018; Abdelazeem et al. 2022; Sanakousar et al. 2023). Applying the Debye–Scherrer equation (Equation (2)) to evaluate the crystallite size from the most intense peak at 32.1°, it was found to be approximately 27 nm.
(4)
where K is the Debye–Scherer constant, β is the full width at half maximum, is the wavelength, and θ is the Bragg angle.
Figure 3

(a) XRD analysis of biochar and (b) XRD analysis of nanocomposite.

Figure 3

(a) XRD analysis of biochar and (b) XRD analysis of nanocomposite.

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SEM and EDX analysis

Identification of the surface morphology and the surface structure and porosity of the biochar and green synthesized Ag-biochar nanocomposite was effectively executed using the SEM/EDX analytical technique as previously applied by other workers. The SEM micrograph of the biochar, Ag nanocomposite, and MB-loaded nanocomposite is shown in Figure 4(a)–(c), respectively. The SEM images as shown indicated a porous structure in the samples which could be attributed to the evolution of minute volatile molecules such as methane and water in the carbonization process (Ahmad et al. 2021; Abdelazeem et al. 2022). The appearance of white patches on the surface of the Ag nanocomposite but not found in the original biochar confirmed the impregnation of the AgNps onto the surface of the biochar by complexation, an indication of successful biogenic fabrication of the Ag-P. saintilinoides leaf biochar-extract nanocomposite. Evaluating the EDX analysis (Figure 5(a)–(c)) for biochar, nanocomposite, and silver-loaded nanocomposite indicate the appearance of strong signals for silver at 3 and 3.3 keV (Figure 5(b)) and is consistent with other studies (Abdelazeem et al. 2022). The percentage of zero-valent Ag in the nanocomposite (3.85%) was interestingly close to the silver ions initially dispersed on the biochar (3.84%) during nanocomposite preparation, an indication of the exceptional biogenic effectiveness of P. saintilinoides leaf extract in the reduction of Ag ions to form AgNPs.
Figure 4

SEM micrograph of (a) biochar, (b) nanocomposite, and (c) MB nanocomposite.

Figure 4

SEM micrograph of (a) biochar, (b) nanocomposite, and (c) MB nanocomposite.

Close modal
Figure 5

(a) EDX analysis of biochar. (b) EDX analysis of nanocomposite. (c) EDX analysis of MB nanocomposite.

Figure 5

(a) EDX analysis of biochar. (b) EDX analysis of nanocomposite. (c) EDX analysis of MB nanocomposite.

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Photocatalytic studies on the nanocomposite

The results of the photocatalytic experiment using an Ag-biochar nanocomposite to degrade MB (0.001 M) under natural sunlight at different time intervals of 20, 40, 60, 80, and 100 min are as follows: 96.32, 95.67, 95.23, 97.29 and 96.48% degradation, respectively. The high percentages of degradation suggest that the nanocomposite is capable of efficiently breaking down MB over time. The relatively high percentages of degradation across the different time intervals indicate that the Ag-biochar nanocomposite consistently exhibits strong photocatalytic activity (Figure 6(a)). The highest degradation percentage was observed at 80 min (97.29%), indicating that this might be an optimal exposure time for the photocatalytic process. Beyond this point, the degradation percentage slightly decreases at 100 min (96.48%). The consistency of degradation percentages suggests that the Ag-biochar nanocomposite is stable over the tested time intervals. Stability is crucial for practical applications, as it ensures that the photocatalyst can be reliably used over time. The synergistic effect of the Ag-P. santilinoides leaf extract nanoparticle and biochar could be responsible for the increased photocatalytic degradation efficiency. When compared with other studies (Abdelazeem et al. 2022) involving Ag@biochar nanocomposite of Chenopodium ambrosioides leaf extract and biomass, it was discovered that the time for the highest degradation of MB for the present work is lower, establishing a higher stability. Kinetically, the rate constant was evaluated as 0.008 min−1 (Figure 6(b)) which was very close to similarly photosynthesized Ag@nanocomposite as well as chemically synthesized AgNPs with values of 0.0147 and 0.011 min−1, respectively (Abdelazeem et al. 2022). The Ag-biochar nanocomposite photosynthesized was implicated to be the source of electrons and hydroxyl free radicals which induce the photodegradation of MB. As a consequence, the nanofabricated product based on these findings can be effective in environmental remediation, such as water treatment or wastewater remediation, considering the high degradation rates observed.
Figure 6

(a) UV-Vis degradation spectra of MB at different time intervals (a) (0.001 M MB). (b) Kinetics of degradation of MB (0.001 M MB). (c) UV-Vis degradation spectra of MB at different concentrations. (d) Reusability of the nancomposite.

Figure 6

(a) UV-Vis degradation spectra of MB at different time intervals (a) (0.001 M MB). (b) Kinetics of degradation of MB (0.001 M MB). (c) UV-Vis degradation spectra of MB at different concentrations. (d) Reusability of the nancomposite.

Close modal

The photocatalytic ability of the biosynthesized nanocomposite for the photodegradation of MB was evaluated under natural sunlight using varied concentrations of MB (0.01–0.0001 M). The Ag nanocomposite (5 mg) was allowed under intense stirring in the dark to attain equilibrium and to encourage the migration of the MB molecules into the nanocomposite matrix before introducing it into the natural sunlight zone for the photocatalytic process. Thereafter, the MB concentration was measured at 640 nm. The maximum photocatalytic efficiency of 93.909% was observed at a concentration of 0.001 M (Figure 6(c)). The percentage of photocatalytic activity decreased at higher MB concentrations as shown in Figure 6(c) probably because of the intense color of the MB which inhibited penetration of the sunlight into the MB Ag nanocomposite mixture. The percentage photocatalytic degradation was however close and indicated some degree of synergy between the biochar and AgNPs that facilitated the ultraviolet light attracting ability of the Ag nanocomposite, a consequence of surface Plasmon resonance phenomenon and the biochar graphitic nature (Abdelazeem et al. 2022). Consequently, ROS are generated as interfacial charge separation gets reduced and recombination electron-hole pairs quenched. The photocatalytic activity of the biochar alone was 10% and the MB was 7.20% further supporting the fact that the photocatalytic activity emanated from the Ag nanocomposite

Reusability of the Ag nanocomposite after desorption with 0.01 M HNO3 indicated that the efficiency decreased continuously from 89.50 to 72% after five cycles of reuse as shown in Figure 6(d). This indicates that the product is photostable and environmentally friendly.

Mechanism of MB removal through photocatalytic adsorption

Based on the FTIR and SEM/EDX results, there are several functional groups present in the Ag-biochar nanocomposite which has the capability of increasing the adsorptive removal of MB as it comes into contact with the surface of the nanocomposite. Similarly, cationic dyes exhibit greater tendencies to adsorb onto the surface of negatively charged surfaces through electrostatic attraction, complexation, cationic exchange, π − π, n − π, and hydrogen bonding between the MB and OH groups resident on the Ag-biochar nanocomposite surface. Similar studies noted that the fast electron transfer process and presence of AgO in the nanocomposite enhances the photocatalytic degradation of MB as the adsorption extends to the visible-light region (Abdelazeem et al. 2022). Consequently, after the initial adsorption that takes place in the dark, there is observed increased removal of MB through a photocatalytic process. The visible light to which the Ag-biochar nanocomposite was exposed generates electron-hole pairs through the SPR phenomenon and reactive oxygen species (ROS) such as hydroxyl radicals through the reaction of free electrons with oxygen and h+ with H2O molecules adsorbed on the Ag-biochar nanocomposite, respectively (Cheng et al. 2020; Mohammed et al. 2021; Balaji et al. 2023; Payel & Debajyoti 2023). These processes trigger the photocatalytic degradation of MB as well as the formation of similar ROS through the interaction between visible light with oxygen as shown in the following equations:
(5)
(6)
(7)
(8)

Comparing the photodegradation ability of the photofabricated nanocomposite with other photocatalysts in some research work indicates that the AgPSBN is highly effective for the photodegradation of organic pollutants such as MB and as such can be used for environmental remediation. The comparison is illustrated in Table 1.

Table 1

Comparison between the degradation capacity/ability of the nanocomposite and other fabricated nanocomposites

CatalystPhotodegradation capacity (%)Dye conc (mg/L)Time (min)References
AgNPs 82.8 60 180 Fairuzi et al. (2018)  
Ag/ZnO 81.2 25 240 Singh & Dhaliwal (2020)  
Ag/ZnO nanocomposite 94.3 10 120 Abdel Messih et al. (2019)  
Ag@biochar nanocomposite 88.4 25 75 Abdelazeem et al. (2022)  
Ag-biochar nanocomposite (AgPSBN) 96.33 25 20 This work 
CatalystPhotodegradation capacity (%)Dye conc (mg/L)Time (min)References
AgNPs 82.8 60 180 Fairuzi et al. (2018)  
Ag/ZnO 81.2 25 240 Singh & Dhaliwal (2020)  
Ag/ZnO nanocomposite 94.3 10 120 Abdel Messih et al. (2019)  
Ag@biochar nanocomposite 88.4 25 75 Abdelazeem et al. (2022)  
Ag-biochar nanocomposite (AgPSBN) 96.33 25 20 This work 

Antimicrobial evaluation of the nanocomposite

The results of antimicrobial studies, particularly the measurement of microbial inhibition zone diameter, provide valuable information about the effectiveness of antimicrobial agents against specific bacteria. The studied microorganisms are relevant; Salmonella is a common pathogen associated with foodborne illnesses; E. coli is a commonly studied bacterium due to its prevalence in food contamination and waterborne diseases; Klebsiella species can cause various infections, including pneumonia and urinary tract infections; S. aureus is a common bacterium responsible for skin infections and can also cause more severe conditions.

In these studies, the microorganisms were coded as C.E (E. coli), C.ST (S. aureus), C.sal (Salmonella) and C.K (Klebsiella). The inhibition zone diameter of the Ag-bio0char nanocomposite against Salmonella, E. coli, Klebsiella, and S. aureus was 15, 12, 10, and 8 mm, respectively (Table 2) whereas that of the biochar alone was 8, 5, 5, and 4 mm for Salmonella, E. coli, Klebsiella, and S. aureus, respectively. These results suggest that the Ag-biochar nanocomposite as an antimicrobial agent is most effective against Salmonella, moderately effective against E. coli, less effective against Klebsiella, and least effective against S. aureus. The variations in susceptibility among different bacteria can be attributed to differences in their cell structures, membrane permeability, and other factors influencing their vulnerability to the antimicrobial agent as stated in similar studies (Akbarzadeh et al. 2018). The observed higher zone of inhibition diameter for the Ag-biochar nanocomposite in comparison to the biochar alone could be linked to chelation theory, a consequence of increased lipophilicity and denaturation of the microbial cell wall (Khan et al. 2020). The interaction mechanism between the antimicrobial agents (Ag-biochar nanocomposite and biochar) could be envisaged to involve the liberation of ROS (hydroxyl radical, hydrogen peroxide, superoxide ion) when the microbial cell comes into contact with the antimicrobial product. The ROS are highly deleterious and significantly disintegrate biologically important species in microorganisms such as proteins and lipids (Panchal et al. 2020; Ghosh et al. 2021). A comparison of the antimicrobial potency of the AgPSBN with other nanocomposites revealed that it is effective against common microbes (Table 2, Figure 7). These results are encouraging for potential applications in areas such as food safety, water treatment, and medical settings where controlling bacterial growth is crucial. Further studies, including detailed toxicity assessments and real-world application tests, would be important to evaluate the overall safety and effectiveness of the Ag-biochar nanocomposite.
Table 2

Comparison between the antimicrobial efficacy of the nanocomposite and other nanocomposites

SampleConcentration (mg/mL−1)Bacterial strainMicrobial zone of inhibition (mm)References
Ag/GO nanocomposite Staphylococcus aureus 15 Jeronsia et al. (2020)  
E. coli 19 
Copper/silver titanium oxide nanocomposite (Cu–Ag–TiO20.5 Staphylococcus 21 Ghosh et al. (2021)  
E.coli 16 
Ag@biochar nanocomposite Staphylococcus Resistant Abdelazeem et al. (2022)  
E. coli No growth 
Klebsiella 18 
AgNp embedded guar gum/gelatin nanocomposite 0.5 Staphylococcus 13 Khan et al. (2020)  
E. coli 12.5 
Pseudomonia aeuroginosa 12 
AgPSBN nanocomposite 0.5 Staphylococcus 08 This work 
E. coli 12 
Klebsiella 10 
Salmonella 15 
SampleConcentration (mg/mL−1)Bacterial strainMicrobial zone of inhibition (mm)References
Ag/GO nanocomposite Staphylococcus aureus 15 Jeronsia et al. (2020)  
E. coli 19 
Copper/silver titanium oxide nanocomposite (Cu–Ag–TiO20.5 Staphylococcus 21 Ghosh et al. (2021)  
E.coli 16 
Ag@biochar nanocomposite Staphylococcus Resistant Abdelazeem et al. (2022)  
E. coli No growth 
Klebsiella 18 
AgNp embedded guar gum/gelatin nanocomposite 0.5 Staphylococcus 13 Khan et al. (2020)  
E. coli 12.5 
Pseudomonia aeuroginosa 12 
AgPSBN nanocomposite 0.5 Staphylococcus 08 This work 
E. coli 12 
Klebsiella 10 
Salmonella 15 
Figure 7

Antimicrobial inhibition zone diameter of the AgPSBN.

Figure 7

Antimicrobial inhibition zone diameter of the AgPSBN.

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The photosynthesized AgPSBN was showcased for the first time. The phytochemicals present in the P. saintalinoides were implicated to be responsible for the bioreduction of the silver ions into AgNPs decorated on the biochar surface. The AgPSBN was spherical with a size of 27 nm range. The low band gap energy of the nanocomposite of 1.8 eV is an indication that it is an effective photocatalyst for the degradation of MB and for other energy applications. The percentage removal efficiency of 96.33% indicates high photodegradation ability which remained fairly constant (75%) after five cycle reuse indicating stability of the nanocomposite. The rate constant was evaluated to be 0.008 min−1 and compares favorably with similar works. The nanocomposite indicated high inhibition for Salmonella, E.coli, Klebsiella, and S. aureus with inhibition zone diameters of 15, 12, 10, and 8 mm, respectively. The results strongly suggest the nanocomposite to be an effective environmental decontaminant of dyes as well as microbes.

The authors acknowledge Dr Boniface Oke of the microbiology department at Ebonyi State University, Abakaliki for helping with antimicrobial analysis

All relevant data are included in the paper or its Supplementary Information.

The authors declare that there is no conflict of interest.

Aayush
G.
,
Kajal
K. A.
,
Loveleen
K.
,
Brar
O. P.
&
Pandey
P. R.
2024
Facile synthesis of Mn3O4–ZnO composite for photocatalytic dye removal and capacitive applications
.
Materials Chemistry and Physics
313
,
128698
.
https://doi.org/10.1016/j.matchemphys.2023.128698
.
Abdelazeem
S. E.
,
Ahmed
M. A.
,
Mohamed
H.
&
Manal
F.
2022
Novel biogenic synthesis of a Ag@Biochar nanocomposite as an antimicrobial agent and photocatalyst for methylene blue degradation
.
ACS Omega
9
,
8046
8059
.
https://doi.org/10.1021/acsomega.1c07209
.
Abdel Messih
M. F.
,
Ahmed
M. A.
,
Soltan
A.
&
Anis
S. S.
2019
Synthesis and characterization of novel Ag/ZnO nanoparticles for photocatalytic degradation of methylene blue under UV and solar irradiation
.
Journal of Physics and Chemistry of Solids
135
,
109086
.
doi: 10.1016/j.jpcs.2019.109086
.
Ahmad
M.
,
Rehman
W.
,
Khan
M. M.
,
Qureshi
M. T.
,
Gul
A.
,
Haq
S.
,
Ullah
R.
,
Rab
A.
&
Menaa
F.
2021
Phytogenic fabrication of ZnO and gold decorated ZnO nanoparticles for photocatalytic degradation of Rhodamine B
.
Journal Environment Chemical Engineer
69
,
104
725
.
doi:10.1016/j.jece.2020.104725
.
Ahmed
H. N.
,
Ahmed
A. S. A.
,
El-Nasr
T. A. S.
,
Alotaibi
N. F.
,
Chong
K. F.
&
Ali
G. A.
2023
Morphological dependence of metal oxide photocatalysts for dye degradation
.
Inorganics
11
(
12
),
484
.
https://doi.org/10.3390/inorganics11120484
.
Akbarzadeh
A.
,
Kafshdooz
L.
,
Razban
Z.
,
Dastranj
T. A.
,
Rasoulpour
S.
,
Khalilov
R.
,
Kavetskyy
T.
,
Saghfi
S.
,
Nasibova
A. N.
,
Kaamyabi
S.
&
Kafshdooz
T.
2018
An overview application of silver nanoparticles in inhibition of herpes simplex virus
.
Artif Cells Nanomed Biotechnol
46
(
2
),
263
267
.
doi: 10.1080/21691401.2017.1307208
.
Balaji
P.
,
Bhuvaneswari
K.
,
Indrani
M.
,
Mohamad
S.
,
Alsalhi
N. A.
,
Pazhanivel
T.
&
Sakthivel
P.
2023
Designing the heterostructured FeWO4/fes2 nanocomposites for an enhanced photocatalytic organic dye degradation
.
Chemosphere
334
,
138979
.
https://doi.org/10.1016/j.chemosphere.2023.138979
.
Cheng
J.
,
Zhan
C.
,
Wu
J.
,
Cui
Z.
,
Si
J.
,
Wang
Q.
,
Peng
X.
&
Turng
L. S.
2020
Highly efficient removal of methylene blue dye from an aqueous solution using cellulose acetate nanofibrous membranes modified by polydopamine
.
ACS Omega
55
,
5389
5400
.
doi: 10.1021/acsomega.9b0442
.
Dibya
R. R.
&
Hara
M. J.
2023
Facile synthesis of novel Z-scheme GO-modified ternary composite as photocatalyst for enhanced degradation of bisphenol-A under sunlight
.
Journal of the Taiwan Institute of Chemical Engineers
147
,
104914
.
https://doi.org/10.1016/j.jtice.2023.104914
.
Fairuzi
A. A.
,
Bonnia
N. N.
,
Akhir
R. M.
,
Abrani
M. A.
&
Akil
H. M.
2018
Degradation of methylene blue using silver nanoparticles synthesized from imperata cylindrical aqueous extract
.
IOP Conference Series: Earth and Environmental Science
105
,
012018
.
doi:10.1088/1755-1315/105/1/012018
.
Fikadu
T. G.
,
Mesfin
A. K.
,
Megersa
W. S.
,
Dinsefa
M. A.
,
Newayemedhin
A. T.
&
Fekadu
G. H.
2023
Facile synthesis of different metals doped α-PbO nanoparticles for photocatalytic degradation of methylene blue dye
.
Physica Scripta
98
(
6
),
065701
.
https://doi.org/10.1088/1402-4896/acd0e3
.
Fong
W. M.
,
Affam
A. C.
&
Chung
W. C.
2020
Synthesis of Ag/Fe/CAC for colour and COD removal from methylene blue dye wastewater
.
International Journal Environment Science Technology
17
,
3485
3494
.
Ghosh
M.
,
Mandal
S.
,
Roy
A.
,
Paladhi
A.
,
Mondal
P.
,
Hira
S. K.
,
Mukhopadhyay
S. K.
&
Pradhan
S. K.
2021
Synthesis and characterization of a novel drug conjugated copper-silver-titanium oxide nanocomposite with enhanced antibacterial activity
.
Journal of Drug Delivery Science and Technology
2021
(
62
),
102384
.
doi:10.1016/j.jddst.2021.102384
.
Ihedioha
T. E.
,
Asuzu
I. U.
,
Anaga
A. O.
&
Ihedioha
J. I.
2019
Hepatoprotective and antioxidant activities of Pterocarpus santalinoides methanol leaf extract
.
African Journal of Pharmacy and Pharmacology
13
(
18
),
359
373
.
https://doi.org/10.5897/AJPP2020.5143
.
Jeronsia
J. E.
,
Ragu
R.
,
Sowmya
R.
,
Mary
A. J.
&
Das
S. J.
2020
Comparative investigation on Camellia sinensis mediated green synthesis of Ag and Ag/GO nanocomposites for its anticancer and antibacterial efficacy
.
Surfaces and Interfaces
21
,
100787
.
doi:10.1016/j.surfin.2020.100787
.
Jitendra
J.
,
Yogita
P.
,
Yogesh
W.
,
Harishchandra
S.
,
Nishad
P. S.
,
Walke
H. F.
,
Chiaki
T.
,
Ratna
C.
,
Shrikant
C.
,
Suresh
W.
&
Gosavi
D. J. L.
2023
Vanadium oxide nanofibers as efficient photocatalysts for degradation of methylene blue under sunlight
.
Journal of Materials Science: Materials in Electronics
34
,
27
.
https://doi.org/10.1007/s10854-023-11127-w
.
Khan
N.
,
Kumar
D.
&
Kumar
P.
2020
Silver nanoparticles embedded guar gum/gelatin nanocomposite: Green synthesis, characterization and antibacterial activity
.
Colloid and Interface Science Communications
35
,
100242
.
https://doi.org/10.1 016/j.colcom.2020.100242
.
Mohammed
N.
,
Jae
H. K.
,
Hee-Young
L.
&
Sung
K. C.
2021
Development of three-Dimensional nickel–Cobalt oxide nanoflowers for superior photocatalytic degradation of food colorant dyes: Catalyst properties and reaction kinetic study
.
Langmuir
37
(
44
),
12929
12939
.
https://doi.org/10.1021/acs.langmuir.1c01999
.
Mustafa
S.
,
Filiz
B.
&
Merve
O.
2023
Treatment of automotive paint wastewater: Photocatalytic degradation of methylene blue using semi-conductive ZrO2
.
International Journal of Automotive Science and Technology
7
(
4
),
316
324
.
https://doi.org/10.30939/ijastech..1378268
.
Nima
M.
,
Reza
D.
,
Masoud
F.
,
Morteza
B.
&
Mahmoud
E. K.
2024
Anodizing of commercial galvanized mesh followed by electroless decorating of Ag nanoparticles for application as novel and low-cost photocatalyst for degradation of both dye and microbiological pollutants
.
Journal of Photochemistry and Photobiology A: Chemistry
447
,
115257
.
https://doi.org/10.1016/j.jphotochem.2023.115257
.
Nworie
F. S.
,
Nwabue
F.
,
Ikelle
I.
,
Ogah
A.
,
Elom
N.
,
Ilochi
N.
,
Itumoh
E.
&
Oroke
C.
2018
Activated plantain peel biochar as adsorbent for sorption of Zinc (II) ions: Equilibrium and kinetic studies
.
Journal of the Turkish Chemical Society, Section A
5
(
3
),
1257
1270
.
https://doi.org/10.18596/jotcsa.438332
.
Nworie
F. S.
,
Mgbemena
N.
,
Nwanneka
U. D.
,
Ikelle
I. I.
&
Mgboh
V. O.
2023
Green hydrothermal synthesis of Ag@Guajavapsidium leaf biochar nanocomposite and the evaluation of the photocatalytic and antimicrobial activities
.
Journal of the Chemical Society of Nigeria
48
(
6
),
1184
1192
.
https://doi.org/10.46602/jcsn.v48i6.944.
Panchal
P.
,
Paul
D. R.
,
Sharma
A.
,
Choudhary
P.
,
Meena
P.
&
Nehra
S. P.
2020
Biogenic mediated Ag/ZnO nanocomposites for photocatalytic and antibacterial activities towards disinfection of water
.
Journal of Colloid and Interface Science
2020
(
563
),
370
380
.
doi: 10.1016/j.jcis.2019.12.079
.
Sanakousar
F. M.
,
Vidyasagar
C. C.
,
Shikandar
D. B.
,
Victor
M.
,
Jiménez Pérez
M.
,
Viswanath
C. C.
&
Prakash
K.
2023
Thermal decomposition synthesis of cylindrical rod-like MoO3 and irregular sphere-like Ag2MOO4 nanocrystals for accelerating photocatalytic degradation of industrial reactive dyes and biosensing application
.
Journal of Environmental Chemical Engineering
11
(
2
),
109371
.
https://doi.org/10.1016/j.jece.2023.109371
.
Singh
J.
&
Dhaliwal
A. S.
2020
Plasmon-induced photocatalytic degradation of methylene blue dye using biosynthesized silver nanoparticles as photocatalyst
.
Environmental Technology
41
,
1520
1534
.
doi: 10.1080/09593330.2018.1540663
.
Suresh
C. B.
,
Maneesha
P.
,
Kailash
S. D.
,
Dilip
S. D.
,
Koyal
S. S.
,
Vaishnavi
B. R. K.
,
Arup
D.
&
Somaditya
S.
2024
Enhanced photocatalytic degradation of organic pollutants in water using copper oxide (CuO) nanosheets for environmental application
.
JCIS Open
16
,
100102
.
https://doi.org/10.1016/j.jciso.2024.100102
.
Tank
R. S.
,
Rowan
R. K.
,
Katherine
L.
,
Thompson
S. E.
,
Aksoy
B. C.
,
Amit
K. S.
,
Raymond
E. S.
&
Ufana
R. F. Y.
2024
Transition metal-doped CuO nanosheets for enhanced visible-light photocatalysis
.
Journal of Photochemistry and Photobiology A: Chemistry
448
,
115356
.
https://doi.org/10.1016/j.jphotochem.2023.115356
.
Yousaf
H.
,
Mehmood
A.
,
Ahmad
K. S.
&
Raffi
M.
2020
Green synthesis of silver nanoparticles and their applications as an alternative antibacterial and antioxidant agents
.
Materials Science and Engineering C
112
,
110901
.
doi: 10.1016/j.msec.2020.110901
.
Zakarya
Z.
,
Nadra
D.
&
Tahar
S.
2024
Sheet-like G-C3N4 for enhanced photocatalytic degradation of naproxen
.
Journal of Photochemistry and Photobiology A: Chemistry
446
,
115189
.
https://doi.org/10.1016/j.jphotochem.2023.115189
.
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