1 Introduction

The need for clean water for living bodies and nature is increasing day by day due to the high population growth and unconscious industrial activities. Higher than 1.0 × 105 tons of pigments and dyes are globally produced each year and it has been stated to be major contributor to water pollution compared to other pollutants [1]⁠. In the dyeing processes of textile industry, almost 10–15% of the dye is missing each year, and releases in wastewater [1, 2]. Other toxic pollutants in water resources, such as heavy metals, drugs, pesticides, industrial chemicals, surfactants, etc., also damage the ecological balance, increase environmental pollution dramatically, and hence adversely influencing biological living systems [3, 4]. To prevent water pollution and facilitate access to clean usable water around the world, it is crucial to reduce domestic or untreated industrial effluents polluting our water resources or take protective measures.

Various techniques, such as adsorption, ion exchange, biological treatment, oxidation, membrane filtration, etc., have been studied for wastewater treatments [5,6,7]. Comparatively, adsorption provides cost-effective, usage ease and simplicity of design; therefore, it is regarded as one of the most influential methods for water treatment processes [8,9,10]. In the adsorption processes, the selection of adsorbent to be used is an extremely significant parameter depending on pollutant types in water and other affecting factors. The most extensively utilized adsorbent for water treatments has been activated carbons because of their considerable adsorption capabilities, various pore structures, alkali and acid resistance, great mechanical strength, and diverse functional groups on their surfaces [8, 11, 12]. To fabricate low-cost activated carbons, agricultural biomass wastes, such as durian shell [13], fern leaves [14], sycamore balls, ripe black locust seed pods, Nerium oleander fruits [15], watermelon rind [16], tobacco stem [17], potato peels [18], almond shell [19], etc., have been used as raw materials in recent years. Usage of agricultural biomass wastes as raw materials in activated carbon productions provides recycling of waste material and economic advantages. Also, the contents of agricultural biomass wastes are hydrocarbons, carbohydrates, lipids, lignin, hemicelluloses, etc., comprising varied functional groups that will provide potentially high adsorption capacity of activated carbon to be produced [20].

Chemical activation using activation agents, such as alkalines, acids, and salts is a successful activation technique to enable improvement of micropore and mesopores, and considerably enhance the surface areas of carbon-based materials [21, 22]. Beside the types of precursors and activation agents, activation agent ratio, application method of activation agents, carbonization temperature, and carbonization duration are other significant factors influencing specific surface area and develop pore structure developments [23]. By considering these influencing factors, activated carbons have been obtained from various biomass waste precursors [24, 25].

In the literature review, Cafer Saka produced activated carbons from acorn shell collected from Quercus petraea usually renowned as sessile oak [26]. Compared to Quercus petraea, Quercus cerris L. (Turkey oak) native to most of western Asia and Europe is one of the different species of oak. Also, the different growth responses of these two species to drought conditions have been seen [27]. Quercus cerris L. is a large, deciduous broadleaf shade fast-growing tree, growing 40–60 feet tall. According to the literature review, it is determined that Quercus cerris acorn shell has not been used for activated carbon synthesis yet. For this reason, the aim of this study is to produce activated carbons from Quercus cerris acorn shell under various experiment conditions, and their characterizations were carried out by using Brunauer–Emmett–Teller (BET) specific surface areas, pore volumes, N2 adsorption-desorption isotherms, pore distributions, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM), elemental analyses, and Boehm titration.

2 Materials and methods

2.1 Materials

Quercus cerris acorn shells (starting material) were collected from an oak tree in Lokvica village (Zhupa region) located in Prizren city in Kosovo. Zinc chloride (ZnCl2, CAS Number: 7646-85-7) was obtained from Merck. Hydrochloric acid (HCl, CAS Number: 7647-01-0), sodium bicarbonate (NaHCO3, CAS Number: 144-55-8), sodium carbonate (Na2CO3, CAS Number: 497-19-8), and sodium hydroxide (NaOH, CAS Number: 1310-73-2) were purchased from Sigma-Aldrich. All chemical reagents utilized in this study were of analytical grade. The brand of porcelain crucibles and capsules used at the carbonization step was Haldenwenger.

2.2 Methods

After Quercus cerris acorn shells collected were washed with tap water and then distilled water to remove dirt, dust, and impurities, they were dried, ground, and sifted with a 50-mesh sieve. Similar method [16] was utilized to prepare activated carbons from acorn shells. The sieved acorn shell as the raw material of the activated carbon in this study was mixed with 80 mL ZnCl2 solution prepared at various concentrations depending on ZnCl2/raw material rates studied. For instance, 8 g acorn shell was treated with 80 mL aqueous solutions at various ZnCl2 amounts of 8, 12, 16, and 20 g under reflux at boiling temperature for 5 h. After the reflux phase, the mixtures taken in the glass petri dishes were placed in an incubator (OF-02), and they were kept at 80 ℃ for 24 h. After that, the mixtures displaced in porcelain crucible were carbonized in a muffle furnace (Protherm furnaces) at various temperature values and carbonization times depending on the parameters to be examined. After carbonization, the activated carbons produced were allowed to cool down in a desiccator, washed with dilute HCL solution (0.5 N) and then distilled water to remove excess ZnCl2 and impurities from activated carbon surfaces by using filter paper. Lastly, the activated carbons (QCACs) were dried at 70 ℃ in the incubator overnight, ground, and stored in glass bottles for their characterizations.

2.3 Characterization techniques of raw material and prepared activated carbons

Thermogravimetric analysis of raw material was completed by using an TGA analyzer (SETARAM instrumentation Labsys Evo). The TGA measurement temperature range was set from 30 to 1000 ℃ with 10 ℃/min temperature increase and 20 mL/min N2 flow. The yields of QCACs obtained were calculated by applying the formula given below.

$$Yield \left(\%\right)=\frac{{W}_{A}}{{W}_{B}}\times 100$$
(1)

where, WA (g) and WB (g) represent the masses of activated carbon obtained and dried starting material, respectively.

BET surface area and porosity measurements of the resultant QCACs were carried out on an automatic apparatus (Micromeritics Gemini VII 2390t) using the BET method [28] by N2 adsorption–desorption isotherms at temperature of liquid nitrogen (77 K) in the relative pressure (p/p0) of 0.25. To eliminate volatile contaminations, the resultant activated carbons were held under N2 atmosphere at 300 ℃ for 2 h before the BET measurements. Total pore volumes were calculated at relative pressure of 0.995, and t-Plot micropore volumes were obtained. Barrett–Joyner–Halenda (BJH) model [29] was utilized to find out pore size distributions. The mesopore volumes were computed by subtraction.

The functional groups on the surfaces of QCACs were studied by using Fourier Transform Infrared Spectroscopy (Perkin Elmer) and Boehm titration methods [30, 31]. According to Boehm titration, 1 g QCAC samples and Boehm reactants (0.1 N 100 mL NaOH, Na2CO3, and NaHCO3) were shaken separately in 250 cm3 Erlenmeyer Conical Flasks with Glass Stoppers for 24 h at 25 ℃. The equilibrated Boehm reactants were filtrated from QCACs, and each 25.00 mL aliquot was pipetted to titrate the excess of base and acid with 0.1 N solutions of HCl or NaOH. The acidic site numbers of QCAC were determined under the assumption that NaHCO3 neutralized just carboxylic acids, Na2CO3 neutralized carboxylic and lactonic, and NaOH neutralized carboxylic, lactonic, and phenolic groups. The basic site number of QCAC was computed from HCl amount reacted with QCAC. Furthermore, the image of sample was analyzed on scanning electron microscope (Zeiss Evo LS 10) to figure out their surface structure. Moreover, elemental compositions (C, H, N, S) of Quercus cerris acorn shell and QCACs were calculated by utilizing an elemental analyzer (Eager 300). Oxygen contents were computed by subtraction.

3 Results and discussion

3.1 Thermogravimetric analysis

TGA, dTG, and heat flow curves of Quercus cerris acorn shell to ascertain general decomposition characteristics during the activation and carbonization are given in Fig. 1. TG weight loss with 6.70% in the temperature range of 40–200 ℃ corresponds the dehydration and the existent of unstable cellulosic components on Quercus cerris acorn shell. The highest weight loses with 61.10% were determined between 200 and 670 °C, indicating that lignin, hemicellulose, and cellulose decomposed thermally [32]. Above 670 °C, weight loses with small amounts showed that the decomposition of some structure in Quercus cerris acorn shell still took place. The peak of heat flow curve at around 350 ℃ shows that the decomposition of Quercus cerris acorn shell is exothermic, while it is endothermic at around 750 ℃. That is because cellulose, lignin, hemicellulose, and other volatile compounds may leave competitively from the structure dependent on temperature values, net energy changes, and thermodynamic properties.

Fig. 1
figure 1

TGA, dTG, and heat flow curves of Quercus cerris acorn shell

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3.2 Yields of activated carbons

Table 1 displays the yields of QCACs obtained from Quercus cerris acorn shell at various production conditions which are different carbonization temperature, carbonization time and impregnation ratio. When holding constant temperature at carbonization temperature of 500 ℃ for constant carbonization time of 90 min., a significant change over the yield of QCAC obtained with different impregnation ratios was not observed. The yield value was calculated around 38%. On the other hand, yield percentage decreased from 40.30 to 31.60 as carbonization temperature increased from 400 to 800 ℃ when using constant impregnation ratio of 2/1 for constant carbonization time of 90 min. Also, carbonization time showed negative effect on QCAC yields by decreasing yield from 39.20 to 35.75% when carbonization time increased. The reason for this decrease in QCAC yield can be explained with having more separation ability of volatile components from the structure when the carbonization temperature and time increase.

Table 1 Yields (%) of resultant activated carbons from Quercus cerris acorn shell at various production conditions
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3.3 BET surface areas of QCACs

High surface area is one of the desired properties for adsorbents as it contributes positively to the adsorption capacity. To obtain an activated carbon with high surface area from Quercus cerris acorn shell, syntheses were performed under various conditions, and the results of their BET surface areas are presented in Fig. 2. One of the factors which affect surface area and other textural properties is impregnation ratio, therefore various impregnation ratios of ZnCl2 were used to determine BET surface areas of QCAC at carbonization temperature of 500 ℃ for 90 min., as given in Fig. 2(a). As ZnCl2/starting material ratio increased from 1.0 to 2.0, BET surface area of QCAC increased from 1356.36 to 1751.61 m2/g. Nevertheless, BET surface area of QCAC decreased to 1630.23 m2/g when the impregnation ratio was increased further to 2.5. Thus, the highest surface area of QCAC in experiments for impregnation ratio effect was obtained as 1751.61 m2/g when used at the impregnation ratio of 2.0 at 500 ℃ for 90 min.

One of the other factors affecting surface area is carbonization temperature due to the needed energy absorbed or released for the interaction of the starting material with ZnCl2 and the release of volatile groups during the carbonization. Figure 2(b) displays BET surface areas of QCAC when synthesized by using constant impregnation ratio of 2.0 at various carbonization temperatures for 90 min. When carbonization temperature increased from 400 to 500 ℃, BET surface area of QCAC increased from 1249.16 to 1751.61 m2/g. On the other hand, BET surface area of QCAC decreased from 1751.61 to 1170.82 m2/g as carbonization temperature increased from 500 to 800 ℃. Hence, the optimum carbonization temperature in experiments for carbonization temperature effect was determined as 500 ℃ when used constant impregnation ratio of 2.0 for carbonization time of 90 min.

Carbonization time is also a significant factor, so QCACs were produced at various carbonization times by holding following parameters constant; carbonization temperature of 500 ℃ and impregnation ratio of 2, and their BET surface area results are presented in Fig. 2(c). When carbonization time increased from 60 to 90 min., BET surface area of QCAC increased from 620.64 to 1751.61 m2/g. This can be explained by the need for sufficient time for the interaction of ZnCl2 and the starting material, and it seems that the carbonization time of 60 min. is not sufficient under these conditions. When carbonization time was increased further from 90 to 180 min., BET surface area of QCAC declined from 1751.61 to 1576.39 m2/g. Also, BET surface areas of the starting material and the activated carbon obtained without ZnCl2 activation were presented in Fig. 2(d) to determine whether ZnCl2 influences surface area. BET surface areas of the starting material and the activated carbon obtained without ZnCl2 usage was measured as 0.54 and 12.55 m2/g, respectively. Overall, in the experiments conducted, the highest surface area of QCAC was determined to be 1751.61 m2/g when utilized at the impregnation ratio of 2.0 at 500 ℃ for 90 min.

Fig. 2
figure 2

BET surface areas of QCACs obtained by using (a) various ZnCl2/starting material ratios at 500 ℃ for 90 min, (b) various carbonization temperatures for 90 min at constant ZnCl2/starting material ratios value of 2/1, (c) various carbonization times at constant carbonization temperature of 500 ℃ and constant ZnCl2/starting material ratios value of 2/1, and (d) starting material and activated carbon obtained without ZnCl2 activation

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3.4 Pore volumes and pore size distributions of QCACs

It is a desirable feature for activated carbon to be enhanced porosity, as it provides its usability as an adsorbent for the adsorption of various substances. While mesoporosity size is significant in the adsorption of liquid phase pollutants, high microporous activated carbons are selected in gas and storage applications [33]. Also, highly mesoporosity is favorable at the adsorptions of metal and organic dye [34]. ZnCl2 is a Lewis acid, has a dehydrating function in activated carbon productions and does not react with carbon, therefore it is used to form an activated carbon with higher porosity and surface area [25]. To examine the pore structure of QCAC, Fig. 3 displays the pore volumes of QCAC produced under various experiment conditions. When impregnation ratio was increased from 1.0 to 2.5, the total pore volume of QCAC increased from 0.761 to 1.473 cm3/g, but the micropore volume of QCAC decreased from 0.228 to 0.022 cm3/g, as seen in Fig. 3(a). Moreover, the mesopore volume of QCAC increased from 0.533 to 1.451 cm3/g, as impregnation ratio was increased from 1.0 to 2.5. When low ZnCl2 ratios are used, ZnCl2 acts as a dehydration agent, causing micropore formation and expansion, while when high ZnCl2 ratio is used, some amount of ZnCl2 remains on the outside of the starting material and decomposes the organic compounds, resulting in the formation of more mesopores and macropores [35].

Using the constant impregnation ratio of 2.0 and the constant carbonization period of 90 min, as seen in Fig. 3(b), the total pore volume (0.707 cm3/g) of QCAC produced at 400 ℃ is lower than that (1.336 cm3/g) produced at 500 ℃, but the micropore volume (0.199 cm3/g) produced at 400 ℃ is higher than that (0.042 cm3/g) at 500 ℃. This may be explained that higher thermal energy makes more active ZnCl2 to expand pore volume. On the contrary, the total pore and the micropore volumes of QCAC reduced from 1.336 to 0.774 cm3/g, and from 0.042 to 0.021 cm3/g, respectively, when carbonization temperature increased from 500 to 800 ℃. This phenomenon is caused by the sintering effect of volatile compounds and carbon structure shrinking at higher temperatures, leading to pore contraction and closure [36].

Carbonization period is also another significant parameter affecting pore volume, and the results are given in Fig. 3(c). By using the constant impregnation ratio of 2.0 and the constant carbonization temperature of 500 ℃, the total pore and micropore volumes of QCAC increased from 0.385 to 1.336 cm3/g and from 0.004 to 0.042 cm3/g, respectively, when carbonization time was altered from 60 to 90 min. On the other hand, the total pore and micropore volumes of QCAC increased from 1.336 to 1.141 cm3/g and from 0.042 to 0.013 cm3/g, respectively, when carbonization time was increased from 90 to 180 min. Moreover, the pore volumes of the starting material and activated carbon produced from carbonization without activation agent are given in Fig. 3(d). The total pore and micropore volumes of the starting material were determined to be 0.001 and almost 0 cm3/g, respectively. The total pore and micropore volumes of the activated carbon produced without ZnCl2 were found 0.014 and 0.001 cm3/g, respectively. These findings proved that ZnCl2 was a significant activating agent in terms of obtaining QCAC with high porosity.

Fig. 3
figure 3

Pore volumes of QCACs obtained by utilizing (a) various ZnCl2/starting material ratios at 500 ℃ for 90 min, (b) various carbonization temperatures for 90 min at constant ZnCl2/starting material ratio value of 2/1, (c) various carbonization times at constant carbonization temperature of 500 ℃ and constant ZnCl2/starting material ratio value of 2/1, and (d) starting material and activated carbon obtained from carbonization without ZnCl2

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When a high adsorption capacity or a productive adsorption process are desired, pore size distribution provides significant information to choose an adsorbent with an appropriate pore size to the adsorbate size. As shown in Fig. 4 presenting pore distributions of QCACs produced, the pore sizes of QCACs were mostly mesopores. It is seen from Fig. 4(a) that the high incremental pore volume values of QCACs are in the range 2 to 10 nm pore width. In this range, the highest incremental pore volume value of QCAC was determined when utilized the impregnation ratio of 2.5/1. Likewise, high incremental pore volume values of QCACs were found out in the range 2 to 10 nm pore width, as presented in Fig. 4(b-c). From the pore distribution data, it was determined that QCACs had mainly narrow mesopores and a very little amount of micropores.

Fig. 4
figure 4

Pore distributions of QCACs obtained by using (a) various ZnCl2/starting material ratios at 500 ℃ for 90 min, (b) various carbonization temperatures for 90 min at constant ZnCl2/starting material ratio value of 2/1, and (c) various carbonization times at constant carbonization temperature of 500 ℃ and constant ZnCl2/starting material ratio value of 2/1

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3.5 N2 adsorption–desorption isotherms

The isotherms in Fig. 5 at a relative pressure of 0 − 0.1 exhibit N2 adsorption-desorption isotherm plots of QCACs achieved under various experiment conditions. According to the International Union of Pure and Applied Chemistry (IUPAC), physisorption isotherms were categorized with six different types [37], and it was developed in later years [38]. The first nitrogen uptake was important in the low-pressure region where p/p0 < 0.1, and the second knee formed in the range of p/p0 > 0.8 for almost all isotherm plots as shown in Fig. 5(a), which specifying the appearance of pore widening process and the mesoporosity improvement [35]. When impregnation ratio was increased from 1.0 to 2.5, the isotherms of QCACs turned into more like type IV(a) from type I. Also, their hysteresis loops resembled H4 type proposing the presence of narrow slit-shaped pores in QCACs [37]. The hysteresis loops enlarged with increasing impregnation ratio, proving more mesopore formation, is also in accordance with the pore volume results because pore volume reduced with increasing impregnation ratio. The hysteresis loops of Type IV isotherms of QCACs are related to capillary condensation become in mesopores and the restricting uptake at high p/p° values, and the first stage of Type IV isotherms was due to monolayer-multilayer adsorption [37].

Like the results obtained from impregnation ratio effect, the isotherm types of QCACs were determined to resemble Type IV and H4 hysteresis type from the results from the effects of carbonization temperature and carbonization period, as seen in Fig. 5(b-c). When carbonization temperature was increased from 400 to 500 ℃, N2 adsorption quantity of QCAC increased. However, N2 adsorption quantity of QCAC reduced when carbonization temperature was reduced from 500 to 800 ℃. These results are compatible with the pore volume results since the highest total volume were determined for QCAC produced at carbonization temperature of 500 ℃. Moreover, N2 adsorption quantity of QCAC increased when used carbonization period was increased from 60 to 90 min. When increasing carbonization period to higher than 90 min., it was determined that N2 adsorption quantity of QCAC reduced and did not change much with even more increasing carbonization time. Thus, it was understood that QCACs produced under various conditions mostly had mesopore structures and their pores were narrow slit-shaped.

Fig. 5
figure 5

N2 adsorption-desorption isotherm plots of QCACs produced by using (a) various ZnCl2/starting material ratios at 500 ℃ for 90 min, (b) various carbonization temperatures for 90 min at constant ZnCl2/ starting material ratio value of 2/1, and (c) various carbonization times at constant carbonization temperature of 500 ℃ and constant ZnCl2/ starting material ratio value of 2/1

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3.6 Functional groups of QCAC by FTIR spectra and Boehm titration

The FT-IR spectra of QCAC and starting material in Fig. 6 were obtained to figure out their surface groups. At the FT-IR spectrum of starting material, the broad absorption peak at 3318 cm− 1 corresponds to O–H stretching vibrations of absorbed water and hydroxyl groups present in starting material, such as alcohols, phenols, and carboxylic groups [39]. The two peaks appearing at 2918 and 2850 cm− 1 are assigned to symmetric and asymmetric stretching C–H vibrations, respectively, in the methyl, methylene, and aromatic methoxy groups [40, 41]. The peak located at 1730 cm− 1 can be due to the C–O stretching and C = O stretching vibrations arising from carbonyl, ester, and ketone groups [39, 40, 42]. The peaks corresponded to the C = C stretching vibrations of aromatic rings are observed at 1610, 1513, and 1442 cm− 1 [40, 43, 44]. The peak at 1369 cm− 1 can be ascribed to C–H deformation in hemicellulose and cellulose or the C–N groups of aliphatic and aromatic amines [45, 46]. The peak at 1315 cm− 1 may be assigned to C–H wagging or phenolic hydroxyl (Ar)O–H [47, 48]. C–O stretching vibrations are observed at 1230 and 1020 cm− 1 [39, 49, 50]. As for the spectrum of QCAC, the peaks at 3565, 3490 and 3458 cm− 1 reveal –OH stretching vibrations due to hydroxyl groups and weakly bound absorbed water [51,52,53]. The band at around 1566 cm− 1 is ascribed to C–C vibration in aromatics groups [54, 55]. The peak at 1155 cm− 1 reveals the presence of C–O vibration [56]. The peaks at 876 and 820 cm− 1 are because of the C–H stretching vibrations in aromatic groups [57, 58]. Also, the peaks between 750 and 500 cm− 1 could be due to C–C stretching and C–H bending [59, 60]. Furthermore, the results of Boehm titration experiments are displayed in Table 2. It is seen that QCAC contains acidic groups as the highest content, almost two times to the basic groups. Among these acidic groups, phenolic groups are the most abundant.

Table 2 Results of Boehm titration (meq/g)
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Fig. 6
figure 6

FT-IR spectra of QCAC and starting material

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3.7 Textural characterization by SEM

The SEM image of the activated carbon with highest surface area was obtained by utilizing scanning electron microscopy to examine the surface morphology of the sample. Figure 7 presents the SEM image of QCAC produced by using impregnation ratio of 2.0 at carbonization temperature of 500 ℃ for carbonization time of 90 min. It is seen that QCAC is a highly porous material with various cracks, voids, large holes, and channels on the surface of QCAC.

Fig. 7
figure 7

SEM image of QCAC obtained by using impregnation ratio of 2.0 at carbonization temperature of 500 ℃ for carbonization time of 90 min

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3.8 Elemental analyses

The elemental analysis results (N, C, H, S, and O contents) of QCAC prepared from Quercus cerris acorn shells at various impregnation ratios under various carbonization circumstances were showed in Fig. 8. The nitrogen content of the produced activated carbons changed between 1.64% and 3.56%, the carbon content changed between 62.66% and 78.58%, the hydrogen content was between 0.71% and 2.45%, the sulfur content was between 0% and 0.26% and the oxygen content varied between 16.23% and 33.24%. The highest carbon content (78.58%) of QCAC was obtained by using ZnCl2/starting material ratio of 2.0 at 500 ℃ for 90 min. Moreover, as given in Fig. 8(d), the carbon content of QCAC produced without ZnCl2 activation was 71.84%, while the carbon content of starting material without any activation and carbonization was determined to be 43.20%.

Fig. 8
figure 8

Elemental analysis results of QCAC synthesized by using (a) various ZnCl2/starting material ratios at 500 ℃ for 90 min, (b) various carbonization temperatures for 90 min at constant ZnCl2/starting material ratios value of 2/1, (c) various carbonization times at constant carbonization temperature of 500 ℃ and constant ZnCl2/starting material ratios value of 2/1, and (d) starting material and activated carbon produced without ZnCl2 activation

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4 Conclusions

Preparation and characterization of activated carbons obtained from Quercus cerris acorn shells with ZnCl2 chemical activation by using various production conditions were demonstrated in this study. The influence of carbonization temperatures (400–800 °C), carbonization period (60–180 min.) and impregnation ratios (1.0–2.0) on the activated carbon yields, surface areas, pore developments, and N2 adsorption–desorption isotherms were examined. The QCAC yields reduced with increasing carbonization temperature and carbonization period. The highest surface area of QCAC was determined to be 1751.61 m2/g when utilized at the impregnation ratio of 2.0 at 500 ℃ for 90 min. The carbonization temperature, carbonization period, and impregnation ratio had an important effect on the pore characteristic developments of QCAC. When impregnation ratio was increased, the total pore volume of QCAC increased, but the micropore volume of QCAC decreased. The pore distribution data showed that QCACs had mainly narrow mesopores and a little amount of micropores. From the N2 adsorption–desorption isotherm data, QCACs obtained under various conditions mostly had mesopore structures and their pores were determined to be narrow slit-shaped. Also, the data obtained from FTIR, Boehm titration, SEM, and elemental analysis provided more information about QCACs produced. Quercus cerris acorn shells can be effectively utilized as a starting material for activated carbon preparation by ZnCl2 chemical activation, and the resultant activated carbons might be utilized for efficiently wastewater treatments. For this reason, our next work will be to test the adsorption performance of QCACs towards impurities in aqueous solutions.