## 4 Conclusions  
Biochars were generated from _Macrocystis pyrifera_ for the first time through a slow pyrolysis process at three temperatures (300, 450, and 600 \({}^{\circ}\)C), obtaining high yields, high ash contents, and the presence of calcium carbonate in all biochar samples. The pyrolysis temperature improves the structural and physicochemical properties of biochar for copper adsorption from 300 \({}^{\circ}\) to 450 \({}^{\circ}\)C, but insignificant differences were obtained in the range of 450-600 \({}^{\circ}\)C. However, at a higher pyrolysis temperature, a decrease in functional groups was observed through FTIR analysis. According to the Langmuir isotherm and mean free energy (\(E\)), the Cu\({}^{2+}\) adsorption from aqueous suspensions occurs through a chemisorption process. The fitting of kinetic models was highly dependent on the structural properties of the biochars. The Cu\({}^{2+}\) adsorption on BC450 and BC600 was adjusted to a pseudo-first-order model, whereas BC300 was explained by a pseudo-second-order model. Both liquid film diffusion and intra-particle diffusion were the limiting steps of Cu\({}^{2+}\) adsorption; however, the surface diffusion in BC300 and BC600 was more important than in BC450, in agreement with their higher pore size. Further studies are required to explore other mechanisms involved in controlling heavy metal removal from aqueous solutions using these seaweed biochars. Thus, biochar from _M. pyrifera_ generated at 450 and 600 \({}^{\circ}\)C has significant potential for use as a bioadsorbent for the removal of Cu\({}^{2+}\) from wastewater or drinking water.  
The following are available online at [[https://www.mdpi.com/article/10.3390/app11199223/s1](https://www.mdpi.com/article/10.3390/app11199223/s1)]([https://www.mdpi.com/article/10.3390/app11199223/s1](https://www.mdpi.com/article/10.3390/app11199223/s1)), Figure S1: Linear isotherm of N\({}_{2}\) adsorption-desorption of BC300. The line with cross represents the adsorption and with circle the desorption curve of N\({}_{2}\), Figure S2: Linear isotherm of N\({}_{2}\) adsorption-desorption of BC450. The line with cross represents the adsorption and with circle the desorption curve of N\({}_{2}\), Figure S3: Linear isotherm of N\({}_{2}\) adsorption-desorption of BC600. The line with cross represents the adsorption and with circle the desorption curve of N\({}_{2}\); Figure S4: pH\({}_{\rm{P}ac}\) obtain of BCs by drift method.  
Project conception, L.C.-P., E.G.-R., and M.A.; experimental design, L.C.-P., M.A., and E.G.-R.; performance of experiments, M.A., C.E.-G., G.S., and J.R.; material preparation, data collection, and analysis, L.C.-P., E.G.-R., M.A., C.E.-G., G.S., E.B., N.E., and J.R.; writing--original draft preparation (and commented on afterwards), M.A., J.R., A.M., S.L., E.G.-R., R.G., and L.C.-P.; writing--review and editing, M.A., J.R., A.M., E.G.-R., R.G., and L.C.-P. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This study was funded in Chile by ANID FONDECYT 1170881, ANID PIA/BASAL FB0002, and ANID Millennium Science Initiative Program ICN 2019_015.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Derived data supporting the findings of this study are available from the corresponding author ([PERSON]) on request.  
**Acknowledgments:** We thank ANID/FONDECYT 1170881, ANID PIA/BASAL FB0002, FONDECQUIP EQM 160070, and ANID Millennium Science Initiative Program ICN 2019_015 for the funding awarded for the completion of this work. We thank LEBMA (www.lebma.cl) for technical assistance, and our friends from Caleta Horcon and Caleta Maitencillo for their support during the harvest of the _M. pyrifera_ biomass.  
**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.