A novel approach for recycling agricultural wastes in the synthesis of nanomaterials and their composites

In this study, main focus has been drawn on the utilization of agricultural waste sources to synthesize nanomaterials. Graphene oxide and nanocellulose were prepared using rice husk ash and sugarcane bagasse, respectively. Further, their nanocomposites were also prepared in (1:1) ratio of graphene oxide and nanocellulose. The synthesized nanomaterials from agricultural waste were compared with those prepared from conventional sources through varied characterizations. Scanning electron microscopy, transmission electron microscopy, fourier transform infrared spectroscopy and N2 adsorption-desorption analysis was performed to examine the structural, functional and surface properties of the prepared nanomaterials from different precursors. High resolution imaging revealed better structural characteristics of the nanomaterials fabricated from agri-waste precursors. SEM images showed well exfoliated structure of GO and porous nature of NC. The folded layers of GO represent the presence of hydroxyl groups in the TEM images of GO @ graphite powder. TEM images of nanocellulose showed circular shaped nanoparticles of NC @ cellulose powder. Fourier transform infrared spectroscopy confirmed the presence of all the essential functional groups in the structure of prepared nanomaterials. The nanocomposites prepared using agricultural waste sources and conventional sources were inspected by N2 adsorption-desorption analysis, which demonstrated that the nanocomposites prepared from agri-waste sources exhibits much higher specific surface area than that of prepared from conventional precursors. R2 possess specific surface area of 82.832 m2 g−1 while, R1 possess only 6.721 m2 g−1. N2 adsorption-desorption analysis revealed the pore volume, pore diameter, micropore volume, micropore area and surface area of the prepared nanocomposites. The nanomaterials prepared using agricultural waste products shows desirable characteristics in all aspects which makes them equally applicable in energy storage devices, food packaging, drug delivery systems, nanosensors and water filtration systems.


Introduction
Agricultural waste is defined as undesirable by-products of agricultural operations and tasks.Waste generation is probably inevitable during any agricultural process.Improper agricultural waste disposal can harm both the human and environmental health.In recent years, bio-based economies and the utilization of renewable biomass as raw materials have been viewed as feasible solutions to the problems associated with regional and global pollution.Synthesis methods of many nanomaterials includes toxic and expensive chemicals, high energy requirements, low conversion, and wasteful purifications and therefore, researchers are finding more innovative ways to utilize agricultural wastes in the fabrication of various nanomaterials as a raw source.Recycling of agricultural wastes into valuable nanomaterials provides additional advantage in terms of circular bioeconomy.
In this work, rice husk and sugarcane bagasse have been utilized in the preparation of graphene oxide (GO) and nanocellulose (NC), respectively.Graphene is a 2-D allotrope of carbon which is mainly composed of tightly packed single layer of carbon atoms, forming honeycomb lattice.Geim and Novoselov were the first who secluded graphene in the university of Manchester in 2004 [1] and received Nobel Prize in 2010 for this great discovery.It has attracted much attention in the recent research innovations due to its structural geometry, which is made of one-particle thick planar sheet of hexagonally displayed sp 2 carbon atoms.Graphene exhibits very outstanding properties such as optical transparency, high electrical conductivity (80 × 10 6 S m −1 ), high thermal conductivity (5000 Wm −1 K −1 ) and excellent mechanical strength.GO is graphene's oxidized counterpart.Graphene is chemically modified with oxygen containing functional groups such as epoxides, alcohols, and carboxylic acids to obtain GO and chemical analysis reveals a carbon to oxygen ratio of about 3:1.GO due to its surface functional groups owes to a unique combination of properties such as high tensile strength, physical and chemical stability, large specific surface area, electron mobility, and heat transfer, has caught the interest of a global research community in the past few decades.Because of the presence of oxygen functional groups, GO disperses easily in organic solvents, water, and other matrixes.Because of the disruption of its sp 2 bonding networks, GO acts as an electrical insulator in terms of conductivity.GO has the potential to use it as a mediator in the fabrication of single or few-layer graphene sheets.Rice husk is an agricultural residue abundantly present in rice producing countries.Around 20 million tons of rice husk is produced throughout a year by the India only.Rice husk mainly consists of 39.8%-41.1% carbon, 5.7%-6.1% hydrogen, 0.5%-0.6%oxygen, 37.4%-36.6%nitrogen and some other minor constituents [2].In this process, rice husk ash (RHA) used as an alternative to graphite powder.KOH was used as an activating agent in this process used to activate RHA.Utilization of rice husk in the green production of graphene oxide leads to circular economy and prevents use of toxic chemicals.
Cellulose is the oldest and most plentiful polymer on the Earth [3] which was discovered and isolated by Anselme Payen in 1838 [4].It is an organic compound having chemical formula (C 6 H 10 O 5 )n.It is a homopolysaccharide with a high molecular weight made up of b-1,4-anhydro-D-glucopyranose units [5].NC has distinct types: cellulose nanocrystals, cellulose nanofibres, microcrystalline cellulose, bacterial cellulose and spherical cellulose.Because of its natural availability, renewability, biodegradability, and intrinsic biocompatibility, cellulose has resurfaced with fresh attention during the last two decades.NC is a nanostructured material made from natural fibres, wood, food processing waste, agricultural wastes, cotton, and other lignocellulosic resources, among others.Cellulose can be converted into NC by doing its acid hydrolysis.However, due to the low acidity of organic acid, the hydrolysis reaction must be conducted at higher temperatures for longer times to improve its hydrolysis efficiency.The hydronium ion enters the amorphous portions of cellulose chains during acid hydrolysis and eases the hydrolytic cleavage of glycosidic linkages.To prevent agglomeration, a mechanical treatment for NC dispersion, such as sonication, is necessary.Additionally, the presence of anion groups causes the creation of a negative electrostatic layer on the surface of the nanocrystals, which aids in their dispersion in water.However, it reduces agglomeration and decreases nanoparticle thermostability.These nanoparticles, on the other hand, have high aspect-ratio, rod-like nanocrystals, and their geometrical dimensions vary depending on the source of cellulose and hydrolysis processes.The advantages of using renewable materials such as NC are that they can replace plastic and metal substrates in a wide range of applications, reducing pollutant residues in the environment.NC can be easily synthesized from bacteria, algae, plant and its residues and tunicates/animals.Various agricultural waste sources such as sugarcane bagasse (SCB), wheat straw, rice straw, vegetable and fruit peels, saw dust, banana rachis, maize husk and corn stalk can be utilized as a raw material to fabricate cellulose and then NC by taking it into the nanoscale.In general, 5.4 × 10 8 dry tons of sugarcane are heavily processed each year to extract sugar juice which produces around 280 kg of SCB from one ton of sugarcane [6].About half of the bagasse produced is used as a fuel to generate heat and power to run sugar mill, ethanol, and distillery plants, with the rest usually stockpiled, posing an environmental risk due to the risk of spontaneous combustion of the bagasse.SCB mainly consists of cellulose, hemicellulose and lignin.Bagasse contains 40%-50% glucose polymer cellulose, much of which is crystalline in structure.Therefore, due to its composition, ease of availability, circular economy and environmentally friendly nature, SCB has been used as raw source in the extraction of NC.We used NC as a filler to prepare composites of GO.
The prepared nanoparticles fillers with polymeric matrix improve the structural, physiological, and functional properties of composite materials and can be prepared using solution mixing, in situ polymerization and melt blending mechanisms.The uniformity of GO and NC dispersion in the material is affected by the various mixing processes through which their nanocomposites can be prepared, also affecting the properties of the synthesized nanocomposites [7].The isotropic-anisotropic structural properties of NCs, as well as their high aspect ratio, contribute to their reinforcement performance by switching stresses and aiding nanocomposite matrix bonding.NCs are stable and tough because of the high number of hydroxyl oxygen groups and strong intra-inter hydrogen bonding networks.GO is a 2-D amphiphilic molecular with water-insoluble π-domains on its basal-centre plane and water-soluble -COOH groups on its edges.Because of the arrangement of hydrophobic-hydrophilic segments on the basal-centre-edge planes, GO nanosheets can self-assemble and interact with NCs chains to stabilize network system with different covalent and non-covalent bonding as van der Waals interactions [8].The plentiful surface functional groups provide opportunities for satisfactory bonding of NCs bonds to GO nanosheets via non-covalent interactions such as ionic bond formation and hydrogen bond formation.As a result, the inter-intramolecular chain of NCs can increase crosslinking density for GO nanosheets via hydrogen bonding, resulting in enhanced mechanical features of NC-GO nanocomposites.Because of the benefits of NC and GO, NC/GO composites have caught the interest of researchers, and they perform admirably as a nanofiltration membrane [9], conductive film [10], anti-bacterial composite [11], supercapacitor, tissue engineering scaffold [12], proximity sensors [13], and so on.

Experimental section 2.1. Materials
Rice husk was provided by the Food Processing and Engineering Department, PAU, Ludhiana.SCB was obtained from the local market in Ludhiana.Cellulose powder, sulphuric acid, phosphoric acid, potassium permanganate and sodium hydroxide were purchased from Hi media.Hydrogen peroxide, graphite fine powder and potassium carbonate was supplied by Loba chemicals.

Preparation of GO @ RHA
Rice husk of 5 g was weighed and mechanically grounded.The powdered rice husk was treated in a calcination furnace for 2 h at 400 °C.After treating inside the furnace, the collected solid residue was called as rice husk ash.The obtained RHA was chemically activated using KOH powder by mixing them in a 1:2 (RHA: KOH powder) ratio.The mixture of RHA and KOH was compacted in ceramic crucible followed by placing the crucible in the centremost of a larger crucible.After that, the arrangement of crucibles was kept in furnace and the mixture of RHA and KOH was heated for 2 h at 800 °C.After the chemical activation of RHA with KOH powder, it was poured in 50 ml of deionized water followed by magnetic stirring for half an hour for the removal of K + ions residues from the sample.Then, the sample was centrifuged at 3200 RPM for 30 min Further, it was sonicated in 100 ml of deionized water for about 50 min After sonication, the sample was centrifuged for 20 min at 5000 RPM and dried in oven for 24 h at 80 °C to remove moisture.

Preparation of GO @ graphite powder
Modified Hummer's method was employed in the synthesis of GO @ graphite powder.To synthesize GO, 3 g of graphite powder was dissolved in acid mixture of 360 ml conc.H 2 SO 4 and 40 ml conc.H 3 PO 4 (v/v 9:1) under continuous stirring.Graphite intercalated compound was formed by reaction of sulphuric acid with graphite powder.Further, 18 g of KMnO 4 was added into the above mixture under continuous stirring conditions.The solution was stirred for 3-5 days till its colour becomes violet.Afterward, the suspension was cooled down to room temperature.The suspension was mixed with ice cold distilled water (400 ml) containing 3 ml of 30% H 2 O 2 .The colour of solution changed from dak brown to yellow.Then, the solution was sonicated for 2 h to exfoliate GO into single layer.The solid residue was washed with 5% HCl solution by centrifugation for 20 min to remove metal ions.Then, the solid residue was washed 12-13 times with distilled water by centrifugation for 15 min until neutral pH is obtained.A black coloured solid residue was put into a beaker and dried in oven at 60 °C.

Preparation of NC @ SCB
The preparation of NC @ SCB involves two steps: (a) extraction of cellulose from SCB, (b) Acid hydrolysis of cellulose obtained using SCB (a) Extraction of cellulose from SCB: SCB was dried in direct Sunlight for several days.The fibre was finally chopped into small pieces and then, mechanically grounded to become powder.The grounded powder was chemically bleached with 0.735% (w/v) sodium hypochlorite solution (250 ml) at 45 °C with constant stirring for 6 h to separate lignin content from it.The residue of the sample was processed with the help of centrifugation and washed continuously to achieve neutral value of pH.To remove hemicellulose, the neutralised residue refluxed using 150 ml of 17.5% sodium hydroxide for 3 h at 45 °C with continuous stirring.The residue obtained from the above process was further washed till neutral pH is obtained.After that, the sample was set to dry at room temperature for 2-3 days to obtain cellulose.
(b) Acid hydrolysis of cellulose obtained from SCB: Cellulose powder was acid hydrolysed with 77% (m/v) sulphuric acid at a temperature 45 °C-55 °C.Sulphuric acid and cellulose powder were mixed at a fixed ratio 9:1 (H 2 SO 4 : cellulose powder).After the hydrolysis process, ice cold distilled water added to the solution mixture for the purpose of quenching the reaction.In order to cellulose sediments, the sample suspension was centrifuged at 6500 RPM for 25 min followed by multiple washings with distilled, further, the washings were performed with 5% potassium carbonate solution (m/v) until the neutral pH is attained.Then, nanocellulose was obtained by drying the mixture in an oven.
2.2.4.Preparation of NC @ cellulose powder NC @ cellulose powder was fabricated by giving an acid treatment to cellulose powder.Acid hydrolysis of cellulose powder was done with sulphuric acid using the similar protocol as described in the section 2.2.3 (b).
2.2.5.Preparation of GO/NC (1:1) nanocomposite An ultrasonic cleaner was employed to disperse GO @ RHA in distilled water at a concentration of 2 mg per 1 ml for about 2 h.Further, a solid content of 1.5 wt% was taken to prepare suspensions of NC @ SCB and GO @ RHA at a ratio of 1:1.The suspension was stirred for 30 min using a magnetic stirrer at room temperature, followed by ultrasonication process for about 2 h in order to get uniformly dispersed solution.Next, the dispersed solution was poured into a petri dish and dried in oven at 60 °C to obtain a film.Finally, the nanocomposite powder of GO @ graphite powder/NC @ cellulose powder i.e., R 1 is obtained.On similar lines, GO @ graphite powder and NC @ cellulose powder were mixed in its 1:1 ratio to get their nanocomposite i.e., R 2 .

Characterization
The prepared samples were characterized using various spectroscopic and microscopic techniques such as scanning electron microscopy, transmission electron microscopy, fourier transformed infrared spectroscopy and Brunauer-Emmett-Teller.

Scanning electron microscopy (SEM)
The synthesized nanomaterials were viewed under SEM (HITACHI S-3400N), installed at the Electron Microscopy and Nanoscience Lab, PAU, Ludhiana.The prepared nanomaterials were in their powdered form.The solid samples were mounted on aluminium stub using carbon coated tape.Next, all the samples were coated with gold using ion sputter coating method.

Transmission electron microscopy (TEM)
To elucidate the surface morphology and structural characteristics including shape and size, the fabricated nanomaterials were analysed under TEM (Hitachi H-7650) accelerating at 15.0 kV installed at Electron Microscopy and Nanoscience Lab, PAU, Ludhiana.Negligible amount of was taken in an eppendorf and dissolved in distilled water using ultrasonic cleaner, sonicating for one hour to form its stable suspension.A drop of the above prepared suspension put on carbon coated copper grid followed by drying in air to examine under TEM.

Fourier transform infrared (FTIR) spectroscopy
To study the chemical composition of all the samples, FTIR spectra for all the prepared nanomaterials was recorded in the wavenumber range 4000-400 cm −1 using Perkin Elmer Fourier Transform Infrared installed at Central Instrumental Facility, Lovely Professional university, Phagwara, Punjab.For FTIR analysis, 1 mg of the sample was mixed with 100 mg of spectroscopic grade activated KBr with the help of mortar and pestle to produce pellets.The pellets were then placed in the sample holder to record the spectra.

N 2 Adsorption-desorption technique
The surface area and textural properties including pore size, pore diameter and pore volume of the prepared nanocomposites was inspected under BET analyzer (Quantachrome Autosorb-IQ) installed at Sophisticated Analytical Instrumentation Facility, Panjab University, Chandigarh.The samples were degassed for upto 4-5 h at 100 °C before N 2 adsorption analysis, which was carried out at a temperature of −195.8 °C.

Results and discussion
3.1.Fourier transform infrared (FTIR) spectroscopy Figure 1(a) depicts the presence of different functional groups in the structure of GO @ graphite and GO @ RHA.The band at 3259.73 cm −1 associated with the structural C-OH and -COOH groups on the surface of GO or hydroxyl groups due to the water adsorbed on the surface of GO in GO @ graphite powder has shifted to 3200.17 cm −1 in GO @ RHA [14].The peak at 1711.43 cm −1 in GO @ graphite powder which is associated with the C=O stretching vibrations appear at 1708.96 cm −1 in case of GO @ RHA.The peak representing the C=C skeletal vibrations of the un-oxidized graphitic domains or with the stretching deformation vibrations due to water adsorbed on the GO surface observed at 1592.43 cm −1 and 1554.41 cm −1 in the spectra of GO @ graphite powder and GO @ RHA, respectively [15].The peak appearing at 1041.22 cm −1 and 1013.05cm −1 in GO @ graphite powder and GO @ RHA, respectively, is associated with the C-O stretching vibrations of the alkoxy group.The presence of C-H bond vibrations in GO @ graphite powder confirmed by the peak at 577.13 cm −1 has shifted to 454.29 cm −1 in the spectra of GO @ RHA.The recorded spectra indicate the formation of GO and presence of oxygenated functionalities on the surface of graphene.The amplitude of -OH stretching is seen to be reduced in GO @ RHA sample.This might be due to overheating of the sample in furnace, while the production of the sample.
The presence of required functional groups in the structure of NC @ cellulose powder and NC @ SCB is shown in the figure 1(b).The broad band at 3234.54 cm −1 corresponding to the stretching of O-H bond of absorbed water in NC @ cellulose powder appeared at 3412.68 cm −1 in case of NC @ SCB.The carboxylic bond is depicted by the peak at 2917.40 cm −1 and 2932.24cm −1 in the spectra of NC @ cellulose powder and NC @ SCB, respectively.The peak at 1633.00 cm −1 in NC @ cellulose powder confirming the presence of water absorbing O-H bending vibrations in its structure observed at 1633.28 cm −1 in NC @ SCB.The absorption peak at 1102.02 cm −1 and 1167.88 cm −1 is attributed to the stretching vibrations of C-O-C bond in the polysaccharide ring of NC @ cellulose powder and NC @ SCB, respectively.The FTIR plots of NC @ cellulose powder and NC @ SCB were compared with each other.There is slight difference in the peak values of NC @ cellulose powder and NC @ SCB.The absence of peak in the region 1500-1600 cm −1 depicts that lignin content has been successfully removed from SCB due to its bleaching process in NC @ SCB [16].The absence of carbonyl and acetyl functional group is confirmed by the absence of peaks around 1700 cm −1 region which corresponds to the hemicellulose and lignin content in SCB.The presence of other functional groups in the IR spectra of nanocellulose concludes that NC has been successfully fabricated from both the precursors.
The FTIR spectra given in figure 1(c) confirms the presence of various functional groups present in the structure of R 1 and R 2 .In the given spectra, the sharp peaks at almost same wavenumbers (2984.76cm −1 and 2983.58cm −1 ) depicts the presence of stretching vibrations in the C-H group in R 1 and R 2 , respectively.The peak confirming the presence of C=O functional group at 1615.02 cm −1 in R 1 has slightly shifted to 1573.44 cm −1 in R 2 .The peaks at 1401.71 cm −1 and 1398.01 cm −1 in the spectra of R 1 and R 2 respectively, signifies the presence of C=C stretching vibrations in their structure.The vibrations of C-O-C stretching in R 1 Figure 1.FTIR spectra of (a) GO @ graphite powder and GO @ RHA, (b) NC @ cellulose powder and NC @ SCB, (c) R 1 and R 2 .
are observed by the peak at 1061.02 cm −1 whereas, similar peak can be seen at 1071.34 cm −1 in the spectra of R 2 .
In the spectra of R 1 , bending vibrations of =C-H group are observed by the peak at 570.17 cm −1 which has shifted to 612.72 cm −1 in case of R 2 .
Comparison curves of FTIR were plotted for R 1 and R 2 .A similar pattern is observed in both the curves with slight shifting of the peaks.The peaks having sp 2 bonded atoms and oxygen-containing functional groups has slightly shifted towards lower wavenumber in case of R 2 .The shifting occurs as there was already a small variation in the peaks of constituent compounds.The presence of all the required functional groups in R 1 and R 2 gives the evidence in the successful preparation of R 1 and R 2 .The R 1 and R 2 ratios were also analyzed under BET surface area analyzer which shows higher specific surface area for R 2 than R 1 .

Scanning electron microscopy (SEM)
From the SEM micrographs, it can be observed that GO @ graphite powder has layered and agglomerated structure.Some kinkled and wrinkled areas are present in the layers of GO.GO layers are either folded or continuous and individual sheets (shown in figure 2(a)).The images (shown in figure 2(b)) shows that the layers of GO @ RHA are well exfoliated.The SEM micrographs revealed graphene flakes with a rough surface.The activating agent KOH and the high thermal exfoliation process caused changes in the morphological structure of the sheets [17].The SEM images obtained for GO @ RHA are much better than GO @ graphite powder.These images (shown in figure 2(c)) depict the presence of small pores in the structure of nanocellulose.Some of the pores are interconnected.Coagulation of the nanoparticles is also observed.The images (shown in figure 2(d)) indicate the fibrillar network of nanocellulose.This image clearly shows the uniformity of the fibrils formed in the NC.The nanocellulose fibrils are present in n-dimensional hierarchy geometry.Acid hydrolysis of cellulose reduces the crystallinity of the nanocellulose.It possesses a porous structure, as there is increase the contact area between the active material and electrolyte.This feature of the NC @ SCB is very helpful in enhancing the electrochemical performance of the energy storage devices such as supercapacitors [18].

Transmission electron microscopy (TEM)
In addition to planar sheets of GO (shown in figure 3   with a large surface area can be seen with a high-resolution magnification.This is because the activated KOH mixed with the rice husk ash defines the particle microstructures.Furthermore, heating at a high temperature in a calcination furnace results in a material with a larger surface area and better mesoporosity [17].TEM images of nanocellulose in figure 3(c) show circular shaped nanoparticles of NC @ cellulose powder.Amorphous regions are also present in the geometry of NC @ SCB (shown in figure 3(d)).These images show the nanoparticles of nanocellulose in several layers.The images were obtained at various scales.The nanoparticles of NC @ SCB are spherical in shape.The figures shows that NC @ SCB has smooth surface than NC @ cellulose powder.The average diameter of a nanoparticle of NC @ SCB is about 48 nm.3.4.N 2 Adsorption-desorption analysis Figures 4(a) and (b) shows adsorption-desorption curves of R 1 and R 2 , respectively.These are positive isotherms of type IV which demonstrates the presence of mesopores in the structure of the nanomaterials.The type IV isotherm occurs due to capillary condensation.A continuous increase in the adsorption isotherm at relative low pressures shows the presence of no. of micropores appearing in the structure of the nanocomposites.Table 1 gives the BJH desorption and t-plot summary obtained from figures 5(a), (b), 6(a) and (b).The pore diameter and pore volume of R 1 and R 2 is approximately same.R 2 exhibits a much greater surface area of about 82.832 m 2 g −1 than R 1 .The BJH method also confirm the mesoporous nature from the pore size distribution via the desorption branch of the isotherm.A sharp peak at ∼3-4 nm (pore diameter) in figure 5(b) confirms the presence of mesopores present in the structure of R 2 .The absence of this peak in the pore size distribution graph in figure 5(a) obtained from the desorption branch implies that it is an artifact that does not correspond to a true pore diameter.The t-plot summary was collected using DeBoer thickness method.It represents the multilayer formation outside the micropores.The micropore area is the difference between multipoint BET area and external surface area.The intercept of t-plot is converted into liquid volume to get its micropore volume.In figure 6(a), the plot possesses negative intercept which provides evidence that no micropores are present in the structure of R 1 .The micropore volume and area of R 2 are 0.061 c.c. g −1 and 115.244 m 2 g −1 , respectively as inspected by figure 6(b).

Conclusion
After interpreting each and every term involved in this research work, the conclusion has been drawn that the chemical precursors can be replaced by the agricultural waste resources for the fabrication of the nanomaterials.Even, the nanomaterials prepared using agricultural waste precursors show equivalent characteristics as that of synthesized from chemical sources.FTIR spectroscopy confirmed the presence of all the desirable functional groups in the structure of nanomaterials synthesized from agricultural waste sources.High resolution imaging techniques revealed the exfoliated structure of GO @ RHA and n-dimensional fibrillar network of NC @ SCB.The nanoparticles of NC @ SCB possesses average diameter of 48 nm.N 2 adsorption-desorption study show higher specific surface area of R 2 than R 1 .Hence, the nanomaterials prepared from agri-waste precursors can be employed in various applicable areas such as energy storage devices, food packaging, drug delivery systems, water filtration, sensors, and research in this area needs to be encouraged.
(a)), few carbon nanoparticles are also seen under TEM.These carbon nanoparticles are seen to be embedded on the surface of the film.The folded layers of GO represent the presence of hydroxyl groups.The nanoparticles of different sizes are clearly visible in the TEM image.Edges in the image shown in figure 3(b) depicts the proper separation of layers of GO @ RHA.A rough and porous nanostructure

Table 1 .
BJH method desorption and t-plot summary of R 1 and R 2 .